What programming sub-disciplines seem to be trending up in terms of career options?

Unfortunately, Machine Learning.

Everyone here mentioned Data Science and honestly, I see it happening but makes me pretty sad nonetheless. ML has been able to do some pretty cool things but the question I keep asking is: has it been worth it? Google has been one of the biggest proponents of ML and I'll be honest; apps like Maps being able to give directions and projects like Watson at IBM are revolutionary and fantastic. However, on the other hand there are problems the industry has "solved" that didn't need solving in the first place imo. Things like YouTube recommendations and super targeted advertising. A lot of my problem with ML comes down to the data itself. Users are using a service with the intent for the service to do its job, not decide what we want to do. The rise of ML has put the algorithms in control instead of the user, and that's not tech I like using.

DevOps or whatever you'd like to call it; 'site reliability engineer' seems to be the hot new title from where I'm at as a newly-minted one of same, although it seems really to be the latest iteration on "make our app & data infrastructure work" previously known as 'release engineer'. I think that's in large part down it having become more than possible for a solo developer to run enterprise-grade kit for free or nearly so with minimal effort: servers and databases (AWS, Google Cloud, Heroku) version control (GitHub, BitBucket), next-gen build tools (Travis, CircleCI), even metrics (Coveralls, PackageQuality). That's done a lot to bridge the gap between development and administration and made the synthesis of the two a compelling specialization for organizations big enough to need specialists. System administration as a separate discipline is never going to die out but more companies will be trying to hold off on investing in it when they can farm that out to the platforms and hire people who can work on the core product too.

Functional language development is having a moment and I'm hoping it lasts. Odds seem good, but it's still not as easy to find jobs working with these as it is to turn up the old standbys of Java, C#, and PHP.

Data science seems like a gold rush with some really neat things happening and a lot of really stupid things happening. I'm not outright bearish but I wouldn't be surprised if demand for analytics-at-scale were to recede some in the medium term.

Blockchain is an outright bubble. It's about to run into the NoSQL issue of "really, you need to know why you want to use this if you're going to commit" but much, much harder.

Data Science. Data Engineering. AR/VR. Crytptocurrency and blockchain.

If I were in college now getting a degree in CS, I'd be looking at those paths for "things I should be thinking about besides just passing my courses".

Testing
I think, with more number of people vying for jobs in the field of Data Science ( And other closely related fields such as Machine Learning ), the number of people who specialize in testing has reduced. Thus, there is ( according to me ) a huge demand for testers / QA engineers.
Also, I feel that testing does not get as much limelight as the other fields do. A lot of times, any role in testing is viewed as a role that is not very challenging. As more emphasis is being given on TDD, and more programmers are being advised to use it, more people need to be made aware of the importance of testers ( and testing ) in a tech team.

I personally see a huge growth in data science / data analytics.

And this probably will grow. Amounts of user data, IoT metrics are growing and data driven business decisions will be made even more frequently. Also, this drives ML, AI too.

Machine Learning, Front-end/UI Dev, blockchain, Clojure, JavaScript everything, Rust.

Bioinformatics! or more broadly speaking being able to merge computation and noncomputational disciplines - especially in chemistry, biology, and physics.

Web performance optimization. People's attention spans are getting shorter and shorter, while the work required of servers is getting harder and longer. Having good caching strategies, small assets, and fast servers is more important now than ever for SEO and positive user engagement, and having people dedicated to building fast, reliable web experiences is really important. This is a large reason why static site generators have really started to explode over the past couple of years.

None.

Too much hype about everything like FP - older than OO but too much hype about it just lately and people that give you the job still do not care if it's fully FP or not, even so they only care that you can do some FP in mostly OO language.

ML and AI getting a lot of hype (also existed before just getting now a lot of attention) but also a lot of problems. Data collection being in it's way because everything is free while we process your data. Now people started to complain about it but not many are willing to pay for services. It's great to have it but main part where I think it's getting fastest research are these tech giants that process your data.

And finally blockchain, crypto currency and digital banking. So much fuss before, and now you decide what's left. Is it changing future? Not really blockchain could later on but it was mostly used for cryptocurrency which, lets be real, are a bit down lately. Digital banking, sounds good, expect to see some problems with data collection, and security (maybe to pessimistic for this one).

So what now? Do we actually have anything new that we need or just pull out old stuff that wasn't so popular before? More examples: gamification in schools by using tech - mostly web based games, new languages, new frameworks...

Btw some companies are now leaving behind technologies and sub-disciplines out of job posts and mainly focus on how you behave as they don't need another dev that thinks he's Linus by just being rude. Now let's think about that.

ML/AI & Big Data Engineer
Blockchain - Contract (ethereum&others) developer
DevOps specialization in Cloud
More C++ switch to Rust, the others to Golang :))

Depends on how you classify programming sub-disciplines, but demands also follows trends in technology:

• DevOps: this is perhaps the biggest and fastest growing programming sub-discipline, especially to manage things like (cross-)cloud infrastructure, CICD pipelines, container orchestrators ...etc

• Machine Learning: perhaps the second fastest growing programming sub-discipline, because data by itself is useless. You need Data Scientist/Engineers to make sense of this data.

• Application Security: I may be biased on this one, but many organizations are realizing that they not only need to invest in Information Security teams, but also attract Application Security Engineers that have strong mastery of both verticals (software development and information security).

VR/AR. Specially for the web.

While my experience is limited and pure anecdotal, so take this with a grain of salt. The conversations that I have with employers, recruiters, and on a limited number of interviews surround a number of roles expressed here. Addition to those already mentioned there seems to be a lot of interest in experienced database developers; embedded device experience; and functional programming.

Titles that have gained traction lately, are embedded systems engineer; DBAs; and data engineering. Being from the Midwestern United States at a company with a lot of technical debt, I have also seen a need for folks who can support and adapt more mature technologies, so I could see a trend-up for people who know legacy systems.

Speech processing and speech analysis.
Computer Vision processing and analysis.

Devops...

Specifically, asking for devops engineers without knowing exactly what they are asking.