Yeah I'm just really not sure what you want to do. Do you want to rewrite mangos in Erlang, or do you want to switch mangos from ACE to Boost?
The disadvantages are pretty obvious: you are writing it in a language few people on here have even heard of, and making it even less accessible to developers, because then they have to know 2 big and completely different languages instead of 1. I also have yet to see some actual solid examples of why Erlang is a better language for this than C++. The only thing you provided compares one feature that Erlang happens to do well, and is compared with C and not C++, which like Schmoozerd pointed out is much more elegant.
As for the Boost thing, I've never used Boost myself and have never really dug into ACE, so I couldn't say either way. Maybe vladimir or derex or another developer can say more on it. If you want to use Boost with mangos you are free to.
Are you going to work on this?