I understand that you want to remove dominion since none plays it and it's pretty much outdated but don't forget Hide and Seek in customs which is played and is a very fun minigame mode when you want to relax. Maybe just remove the dominion queue but let the map on custom so we can still play it plz 
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Copy pasta from another thread to answer this one:
Unfortunately, keeping Dominion available in Custom games still has the same cost as being a matchmade queue. :/ We have to ensure all champions work with capture points, items, etc.
The art on the map is also far behind what we'd consider the 'quality bar' for League nowadays. It would be a herculean SRU level effort to bring it up to parity (when we could better spend that time/resources doing something awesome on SR instead).
As to re-using the map somehow, that's certainly not off the table (as we mention in the post), just no promises.
