pure theory. Backing up opinions with evidence is for nerds.
I strongly SUSPECT it wouldnt work- firstly because half the time in mvm is spent slowly retreating,m and that becomes a far more viable strategy on a longer map. Plus, it becomes far harder to balance walk times, since they're near enough irrelevant for one team. Plus early rounds are entirely dependent on bots being able to close the distance with players. plus a horizontally wider map is far easier for backcappers.
Listen to this guy ^
doom please, we are trying to squash creativity here. kindly step aside
Ignore this guy ^
My suggestion: While talking about the theory of if it works is great and all, Try it out! Get some friends of yours together, and host a listen server on whoever has the best internet connection. Play it, see how it feels compared to exisiting, stock, MvM maps and then decide "hey, is it really too big?", 'Am I having fun?" etc. And make sure your friends aren't afraid to tell you it sucks, and offer area's for improvement.