I also think it would be a really cool idea for a 1v1 or 2v2 map.
The problem is, apparently no one wants a 1v1 or 2v2 map.
Remember Snowdown Showdown? We got to play 1v1's and 2v2's on Howling Abyss during the Holiday Season in 2013, and apparently it was one of the less popular featured game modes. The data Riot collected from this mode apparently gave them enough evidence to conclude that a dedicated 1v1 or 2v2 map isn't something that most players would actually play, especially considering Howling Abyss already can function as a 1v1 or 2v2 map if you wanted to play a 1v1 with your friends or something like that.
That said, Magma Chamber was really cool, and I personally would have really liked to see it get released in some form.