There's a subtle irony in Riot saying they'd look into putting a ranked mode into dominion the year after it was released, then never doing anything with it.
It's like they're coming out now and saying, "oh man dominion is just too unpopular to support anymore" after never letting a competitive scene thrive there. Crazy.
I actually liked Dominion more than SR by a mile. I remember when it came out I logged something like 300 games before the season ended. It's a much healthier game than "am i strong enough to tower dive then brute-force this tower, or do I have to split push to make sure this objective dies?"
We never even got a draft mode on dominion, did we? Only map mode where you make selective picks without ranked? Probably had the lowest number of reports/toxicity out of any mode, even when it first came out? Riot kind of struck gold and quietly walked away from it with dominion, which is a pity because the whole "farm for 20 minutes" aspect of their game isn't the appealing part of it.