while it does sound nice on paper I think there are major problems here.
1. Converts. Maps designed originally for STD but got converted to other gamemodes. They have a really bad reputation among other gamemodes community - especially mania - due to how bad the quality it is. Maybe with new players you can play them just fine but for a more experienced one it can make them feel like a joke among the match, because the map may not match their skill.
2. Host rotation. What if you tranfer the host to someone who specialized on other gamemodes but STD? High chance they will choose the one fit their skill and even higher chance it's not converts, meaning others who play anything but the gamemode they're in will be fucked. And if it's convert, they'll go back to the situation mentioned in the last sentence of point 1.
I know your intention, but I really doubt on the practicality of this concept.