Yeah, my opinion on this is that the GUI should be separated from the underlying code. BUT... there's no need to throw the baby out with the bathwater and I firmly believe that the current wxWidgets interface should be maintained until such a time as something superior comes along.

My personal feeling is that whilst separate daemon/GUI binaries can work, it also tends to be messy, I'd be far more in favour of having the core code and then separate source that you compile with it according to your target OS, that way everything is still a single binary and can be integrated as idealistically as possible.

To put this in practice, imagine 3 SVN trunks; the first is BitCoin core, the other two are LINGUI and WINGUI - the latter two being dependant on code from the first.