Too many times in the domain world people start regging domains that had no interest to them when they started out. They fall into what I call "domainers trap," meaning they start reading blogs,sales reports and forum posts and start regging domains where they have no interest or expertise. Now it is not bad to be diversified and to learn as much as you possibly can, but don't own 200 different niches when you started out trying to build a portfolio rooted in your personal expertise.
I have had some people tell me they wanted to have a few .XXX domains just to be a part of the fun. But at $85 to $100 a registration, its not fun. They had no interest in .XXX at first but after reading som much about .XXX felt they had to get a few domains. Its easy to fall into the hype because you read about it every day. If you had no interest in .xxx don't register any. If you have real interest then be careful and pick something you think you can make money with.
When there are hundreds of new extensions it will really get crazy. Domainers will wonder should they register a .shop or a .web or .eco. You need to make sure you understand how these extensions roll out, what is being held back for auction, will you have a chance to get a really good name.
Most importantly stick to what you know.