Install pfsense on an existing freebsd install?
can pfsense be installed over an existing freebsd install?
Does pfsense use any binaries other than the freebsd OS underneath?
I want to experiment with installing freebsd ARM on a guruplug and transplanting pfsense on top of that if possible.
No, it cannot be installed that way.
Though once you have FreeBSD installed you could use the pfSense build system to try building on there, but no telling if that might 'just work' or not.
is there a place for feature requests? i dont see one in the forums.
You can open a feature request ticket at http://redmine.pfsense.org/
We're very open to feature requests in general, but in this case if you're going to request the ability to add on top of a stock FreeBSD release, that's going to go to the "needs patch" pile, i.e. it's not going to get any attention from us.
pfSense is a customized OS in itself, there are a few dozen patches to FreeBSD to make it behave better as a firewall and router. The rc system would break everything on a stock FreeBSD. For those reasons, amongst others, we won't ever have the ability to install on top of a stock FreeBSD. There's just way too much difference between the two for that to be remotely reasonable.