If BlockWars shows that it has a large enough player base to support it being a full time game, we'll obviously review it as we have done in the past with other featured games. As of right now, BlockWars (either flavour of it) is not the most popular featured game, but that doesn't mean we aren't going to continue to review the situation.
As for the ability to select maps, this is possible, as a ranked player you right click on your chosen game instead of left click, this will then bring up the map options available. Yes, that does mean that this is a perk locked behind a rank, there are precious few things that can be monetised while staying within the constraints of the EULA, this is one of those and we've made Iron rank cheaper so that getting access to this perk is easier than ever, especially when ranks are on sale.
Edit: I should probably clarify a little on the current best performing featured games... BattleZone (admittedly it's new) -> Survival Games -> Wing Rush -> BlockWars Core