Very interesting post. One thing jumped at me though:
"It started with functional programming, one of the academic topics which has been discussed since the 60s but never took off."
You seem to frequent HN, so surely you must be aware that functional programming actually took off in the end - just now. In the last 5 years it went from something that people would give you strange looks over mentioning, to The Hottest Thing in programming. "Functional" is now synonymous with awesome and something people brag about (whether they understand it or not is another thing, but that's how things are with fashion).
Functional programming is an amazing tool, but I found it super hard to program real world applications. Object oriented programming is much more useful for that, because it represents more effectively the world that we live in, which is composed of objects that talk to each other.
Yes, functional is now cool and awesome and hackerish. Nothing wrong with that. However, while it does make you smarter (since it gives you a new viewpoint and is a new skill), it does not mean that you need to apply it everywhere.
I'll add that us in HN live in a bubble and what we read here is not representative of real world. Of all programmers I know only two really know and have successfully coded stuff with functional programming. So... It has not taken off in my opinion. There seems to be more eyes looking at it, or maybe people using it are more vocal so we read more about it.
If you let me, just choose what your heart says. I know it's a cliché, but for a side project you can't go wrong with doing what intrigues you. Paid work is different, you know, but in your free time you should just choose one thing and go with it, and if for any reason it doesn't succeed, go with the next one.
