@trof
The point here is that you must say that it’s a layer that AFAIK redirects to your Elgg installation.
Elgg is released under GPL license ver.2 so you must do that.
I presume that you’re trying to build some kind of (paid) service in the future.
For now, what you are doing is something that might pose a ridiculously high security breach in each WP it is installed.
That said, you and your friend are very skilled programmers. ??
@asshu
The interface IS Elgg.
Even GRA4.com is a out-of-the-box Elgg installation!
Why don’t you try to install Elgg and see for yourself?
Why not choosing BBpress or IntenseDebate? They’re made BY WordPress…