I don't really get the point here... Why would you like to do that...? I mean, of course the RAM is "not enough" but it is not the GUI that couses problems... Or maybe I'm wrong but that is my experience... And as nonsuch said you would lose functionality...
I use my kali chroot wm with i3 and it is working quite well; but using the whole Maemo 5/n900 that way... for me it is a no-go because "hey, this is a phone and a camera as well". But if you would like to use it (and use it only) as a computer... You can try.