Some people have already looked at the code and determined that there are multiple additional companions that are tagged (including a certain Ranger with a Hamster). Larian still has a year to clean up and modify their code, so by no means should anything be considered final until release.
BTW If Haslin is a potential companion, I imagine his opposite, a certain Drow Priestess, who also joins you in camp, might be as well, since getting the Drow means killing Haslin.
Shadowheart is already an LE Cleric, we don't need another. It would be weird to get the Drow. Also, she doesn't have a unique outfit.
