@vio7 @StupidSelfishNasty @hash11011 @risky-chess is there a particular reason you want 10+5 (or 10+2) instead of 15+5? Or was that just "the first thing that came to mind"?
My reasoning for 15+5 is twofold:
A) Some amount of OTB parity: The FIDE standard Rapid tc is 15+10, so we should aim to have a timecontrol close to that
B) Spread! "Rapid" on lichess is 480-1499 seconds (to move 40); and we have a tc on the very low end of that already (10+0 is 600). 10+5 is 800, which stilll isn't even close to the halfway mark of the Rapid spread (989.5), let alone on the higher end. 15+5 is 1100, so it fits very nicely.
Same reason as to why we have 3+0 (180), 3+2 (260), 5+0 (300) & 5+3 (420) on a 180-479 Blitz scale, rather than 3+0, 3+1, 3+2, and 4+0 (which would be senselessly close to each other).
IMO it makes much more sense to keep the different TCs "as far away from each other as possible", ie having both 10+0 and 10+5 is overkill, and the Rapid increment TC should instead be on the long end (with 15+5 being the current suggestion)
@Toadofsky @erikelrojo (and maybe others): Removing 10+0 is not happening. It's by far the most popular Rapid tc. It's not "only more popular cause it's a simple number", many people just dislike playing with increment, and especially for Arenas (where Berserking removes Increment altogether), +0 TCs are actually crucial to have.
I hate playing without increment, but factually it's supremely popular on lichess, so it will (rightfully so!) never get touched.
@Morozov I'm not a big fan of making it 4x4, as that splits the community massively. Already, 2+1, 5+3, and 15+15 aren't played by many people; with 3+2 also comparably inactive, so almost doubling the QuickPlay buttons (going from 8 to 15!) is not really an answer. 1 more is fine, espec as Rapid +Increment is just not represented at all currently, but I wouldn't even know what to fill the rest of the squares up with.