I don't know about
Spelljammer monsters in a ToH2. I mean, I love
Spelljammer, but if there'd be more than a few monsters from that setting, they should go someplace thats distinctive to them. Ideally, the official site would be more organized in official-dom, but that's beyond the scope of this thread. That said, those official SJ monsters can be seen
here.
Other monsters I'd really like to see would be the devilswine, tabaxi, amphisbaena, rakasta, the rest of the linnorm dragons, the living steel...in fact, lets just say all the monsters from 2E's
Monstrous Compendium Annual series...some of those creatures, like the arch-shadows and such, were really great.
And of course, more than anything else I just mentioned, I would like the see the rest of the palanar-alignment races fleshed out! Last I checked, there were...
still a few kinds of tanar'ri left (alkiliths, for example)
I think all the baatezu were converted
there's still plenty of yugoloths to go (including the unique ones)
the gehreleths (though not one of the "big 9") have been taken care of in ToH1
Two Slaad lords remain (Chorst and Renbuu)
The Modrons are completely statted out (save for rules on Rogue Modron PCs)
here
The various celestials (archons, guardinals, and eladrin) all need to be fleshed out badly
and so far, the rilmani (and that other neutral race mentioned in
Tales From the Infinite Staircase) remain as-yet untouched.
That's what I would like to see (sorry so much of that was lacking in specifics).