Honestly, Summoner's Rift is Incredibly Boring After ~3000 Matches
You guys try to keep it fresh from season to season by massively changing the landscape of the game, but at the end of the day it's still the same game. After 3000 matches, I've become very bored with it, especially since each season seems to devolve into the same champions picked on repeat every game. I can't even imagine what players who have played 6000 or more games feel like. This makes me wonder why you would remove Dominion.
Not everyone who played it was a hardcore Dominion player. Some people just played it to take a break from the monotony of SR. I personally only have ~400 matches played on the map, but just the same I feel that removing it is more a detriment to the game than a benefit. There are times when I walk away from League for weeks or months, and Dominion helps me get back into the game because it's a much less punishing environment than SR.
As it is now, I typically only play Dom or 3s if I don't have friends around, because of the sorry state of SR. There's nothing fun about being absolutely crushed after one mistake on your or your team's part. In Dom it wasn't over til it was over, and in 3s there's a LOT more room for one person to carry, mitigating mistakes from individual players on your team.
You say you're eliminating it because of a small playerbase (which is silly, because then you could eliminate champions for the same reason) and wanting to devote more resources to SR. How many resources could Dominion really be taking? You don't balance for it at all, you don't take care of the bot problem at all, the only thing you do is make sure there aren't bugs and that a champion gets capture animations. A large number of interactions are the same between the maps; champ v champ, items on a champ, general graphical things, etc. I can't remember the last time I heard of a Dominion specific bug. Is it so hard to just keep doing what you've been doing and ignore the game mode?
I would rather you ignore it and keep it around to provide an alternative to SR that isn't SR-lite (TT) or ARAMs. I know you won't, because you've already made the decision and once you guys get it into your head that something will be healthy for the game you go ahead and do it regardless of feedback.
When all the bots move to Twisted Treeline (because they will, that or bots) and you continue to ignore that, as you did Dominion for however many years, to come are you just going to scrap that too? You say they are no current plans to do so, but that could easily change. After all, there are TT specific items and interactions that you have to deal with that could be time "better spent" on SR, aren't there?
At any rate, before this turns completely into just a salty rant, that's my two cents.