I said this back at the beginning of march (what the heck I thought I made this joke at least a year ago), but a Promise/Myth merger could actually happen...
I still stand by what I said when I heard of Mumei though; I like holo merch and concerts and stuff, but I'd rather have the ones I like all graduate and hang out behind the scenes than have half-in/half-out. (Yes, I know that thinking that all graduated members will keep in touch is cope)