there was a discussion about that once a few years ago, and I think it does work, but losing a space just to get one more MA & EAC is kind of nuts… unless you build around it.
ok, I just did a Search 
and it looks like Epiphany will increase the Stat Cap of anything except +All Set. it looks like as long as an affix has a Cap and isn’t +All Sets, it will be affected by Epiphany.
that means if you want +5 Multi Attack, it will take 3 spaces, same for Extra Attack Chance, unless you use that MythStone that gives +4 EAC and an Epic EAC to take up only 2 spaces.
I was just doing the math in my head, Epiphany (5) will give a Cap of +5 for MA & EAC, but Epiphany (8) will give a Cap of +6 for MA & EAC.