I played XI and WoW for a while in 2005. The problem that it creates is the fact that one will always interfere with the other just due to the sheer amount there is to do; especially at max level.
If you were going to level up while you were playing another game simultaneously, it'd probably be okay, but once you got to level cap in both games, you'd really be struggling to keep the same amount of interest in both.
but then it still creates the dilemma of
"i can level up simultaneous on these two games and take 2 months hitting max level on both or stick to just one and hit max levelin a month..
also the main problem is subscription fee... if youre paying lets say 15 bucks a month each on two games you start to feel like youre not playing either as much as you think you should based on the money youre investing in them... now if you played 3 MMOs one was subscription based and the other two were F2P hen I dont see a problem.. play the one youre paying for as much as you need/want and you can play the other two whenever you want.. even if that was 4 hours a month lol. at least you wouldnt feel your money was going to waste