But following a play session at Blizzard some weeks ago, I've learned that several of these classic units will still show up in the Wings of Liberty campaign.
The Terran Firebat and Medic will be playable as standard singleplayer units, both unlocked after completing various missions. Fans of the Dragoon may also have some hope of an appearance by the four-legged unit.
During a skirmish round, I encountered a chance bug that allowed me to build a Dragoon from a standard Gateway. The unit's artwork was incomplete, and its icons were carried over from the original game, but there it was regardless.
When asked about the Dragoon sighting, a Blizzard rep told me that the unit was definitely not being added to multiplayer, but rather that it could possibly show up in the singleplayer campaign--no doubt with its "I have returned" line feeling a bit more ironic.
Awesome. It's not Starcraft without the firebats and medics. All the other old classic units will be gravy.
I think they've mentioned that they're planning on releasing all of the old/unused Starcraft units for the editor.