By doing this, transition from Grub to GDM (or KDM or whatever) would be done almost instantly. Plymouth will use a graphical boot mode with a fallback method to text for those computers that don't have hardware support.
When Fedora releases this, and it works OK and better, then I'll vote... 'till then, Fedora seems to be on the forefront of new stuff, only to be riddled with many many bugs from the new stuff right after.
Remember that Fedora doesn't care about closed drivers and until nVidia and AMD (for fglrx) implement some features, Fedora will not start so nice like for Intel/etc.
Seconding @Tuxoid here. @ajjeckmans and @Vadim P., considering Ubuntu is currently perceived by outsiders as not contributing back enough, you might not want to say things that give the perception that you encourage freeloading!
@VisitorQ: plymouth will help things like fast-user-switching, logging in and out, and switching to a virtual terminal as well. And @jrusinek, AMD/ATi support is actually forthcoming. In fact, in the current F10 (rawhide) kernel, only ATi support is enabled because the Intel driver is being reworked upstream.
Plymouth is safe at this point to start testing -- without a modesetting kernel, you get text-based boot anyway.
@slsolaris: I strongly disagree with you. Having every distro reinvent the wheel (and, if Canonical were to follow your advice, invent a cheap copy of it) just makes it harder for distro's and upstream devvers to cooperate, which means that development of nice features as a whole will almost grind to a halt.
Just to let you know, that even without a mode-setting kernel you can get a none text bootup with Plymouth. All I you have to do is pass vga=791 (for example) in the kernel line in your grub.conf
It's rather nice actually, though since I don't have an intel based gfx it's not flicker free