Thank you for your answer !
Yes indeed I was thinking about this.
I've used Proxy Pass and Proxy PassReverse before, but was unable to get 2 services running on port 80 on 2 separate subdomain (Anyway I've to give another try)
I'm not familiar with ISPConfig (yet), but I'll try to use the apache directives field. (I guess it's very easy
Thank you !
PS: Any plan to support that? I'm sure it can be very useful for a lot of people.