( i wonder if another homonid species was found alive if we'd enslave them, it's possible. )
Well, this is of course possible. A bit back (cant remember dates) we enslaved black people to do our work. We are different species I believe, but similar (labrador and bull terrier etc). And in Victorian times the British empire wiped out the tansanians in just 50 years.
Hopefully havn't gotten my facts wrong but my point about this is maybe there could have been hundreds of other types of humans but as you say we have wiped them out. for all we know there could have been people like mantis (green, leaf like extenstions for hiding, claws/jaws for hunting etc)
Cheers, Cameron.