Is it possible to raise the cap up to 100, you think?
It is possible, as the cap was pushed as high as 125 for a while in the past. They played like crap compared to what we have now though.
Increasing player capacity per server is probably not going to happen because it fucks up server performance on both short and long term period, resulting in even more desync issues immediately, and over long term it'll become worse because more players per server increases the amount of objects (storage and other) they leave around which also negatively impacts server side performance. It's not just about the number of players currently on the server, it's also about everything they leave behind. I guess it's not incorrect to say that higher player pop will increase server performance problems exponentially.
If legion servers ever happen and they manage to make them switch maps every three hours, cleaning up everything, I think it could make it possible to run those servers with up to 100 players. Just a hopeful guess though.