The sp1200 would be a little tougher to emulate because each sample slot had different filters to cater for kicks snares and hats.
Also, it used an older technology to pitch drum sounds called sample skipping. Sounds a little different than normal standard pitch shifting.
And as for the 808s it would be nice to get an analog emulation (although probably most 808s you hear are samples) since an actual 808 is an analog unit.
This request isn't high up on my list of things that has to be done (I get by great without it) but I just think it would be cool if someone truly emulated these machines (Maschine has SP1200 and mpc 60 emulations).