Solas can't stand the beings that live now...he considers them to be like Tranquils so I do think he wants anyone dead that will despoil what he thinks would be ideal. He wants to erase the beings that exist now because he considers them to be so unworthy of existence, as if their lives have no meaning because he feels they are inadequate. I do not think things will go as Solas plans since all his plans seem to end in failure. Someone really does need to stop Solas from doing more harm to the world.
If he's friends with the Inquisitor, or romanced by the Inquisitor, he definitely doesn't want everyone dead; he sees them as people and no, does not see them as unworthy of existing. Even if you aren't friendly with him, I've seen it on Youtube... he's very regretful that there's going to be so much chaos and destruction. It's sickening that he still intends to go through with it, and I can't say I feel badly for him (my Inquisitor romanced him and I felt SO BAD for her, because how awful to be told the things he told her...), but the fact remains that killing everyone isn't his intention. He expects it to happen, but he isn't going out of his way to murder everyone.
It's more accurate to say that "fixing whatever is wrong" is more important to him than the lives of basically everyone on Thedas. This probably includes the other ancient elves, in my opinion, because it's inevitable that more than a few of them will also die in the chaos. Some think that this is because Solas is being selfish and just wants to assuage his guilt. I think he believes whatever is wrong, precisely (and I don't know for sure if it has to do with magic, or spirits, or WHAT) with everyone on Thedas, is SO wrong, that he HAS to fix it, regardless of the cost to everyone currently alive. And he hates himself for it (which let's be honest, he should--he's pretty cold to even consider such a thing). If you haven't seen his friend/romanced dialogue from Trespasser, as well as his low approval dialogue, I highly recommend you go find it on Youtube. It's not about wanting everyone to die at all. Whatever his ultimate reasons, they're more complicated than just wanting to kill everything and start over. Otherwise, he'd just be a moustache-twirling villain, and that would be pretty boring and not in line with what I've seen of Weekes' writing.