I know a bunch of you picked up one of those MC-E color LEDs and drivers to match. Now what?
Does anyone have any good host ideas for these? How big are these MC-Es anyway? I have no idea if I should be looking for an XM-L or XP-G size host.
Well, if you are going reflectored then I'd rule out an XP-G host immediately as the dome on the MC-E is huge and the hole in an XP-G reflector is miniscule. Nothing less than and XM-L and even that you will have to ream out to enlarge. Ideally an MC-E or P7 host, possibly even one made for an SST-50 would work well without modifying.
A larger FTT light would be a good option. That 26650 sized SK68 clone comes to mind first and is only $13. One of the guys here shoe-horned that RGB LED and driver into an SK68 somehow and it works well but I'd certainly go with something larger.
If I didn't go with this one, I'd go maybe with a ZY-C10-S or a UF-T20.
I did a build with the sipik sk68: https://budgetlightforum.com/t/-/15561
It now has become easier than that, Intl-outdoor has come out with the MCEcolour on 16mm board and a 17mm driver (I suppose you have those?)
But you can use any of the many single li-ion (14500,18650) hosts with 17mm driver/16mm ledboards now. The led draws 800mA max. so heatsinking is also not much of an issue. I must say I like to have it in a zoomie, that makes it more fun. And fun is the reason to use this led, I haven't come up with any practical use (I like that aspect 
).
MC-E will fit in a P60 pill with XR-E reflector just fine.
If you decide on a zoomie you will not have to adjust a reflector (like JohnnyMac popinted out). But do be carefull that the MCE led sticks out more from the pill, so that it probably will touch the lens when zoomed out (that is easily solved by placing a loose keyring (the size of the pill) in between the moving head and the pill). And you can no longer zoom in fully since the led sticks further out.