That's a shame, got some good memories with Gen 7, and to an extent, Gen 6.
I found GTS and Battle Spot to be somewhat dead in both games, but it's nice to use them once in a while. I will miss Wonder Trade, however, good way to get a lot of good pokemon for basically nothing, you can literally just catch low level pokemon en masse or breed them and go ham.
Lots of people with high end/rare pokemon giving them away because they breed literally hundreds of them for the perfect IV/Nature combo, and there is some cheeky genners who will send over legendary/shiny/competitive pokemon sometimes. All of that will be gone in April, and even if fans restore it Wonder Trade still won't be the same since the whole point is that a whole bunch of people are doing it at the same time as to always have someone to trade with.
Doesn't the Xbox Live Marketplace also shutdown around the same time? I really need to dedicate my time to buy up all the good games left on the marketplace and Wonder Trade/GTS hunt some good pokemon