The Etiquette proposal has a lot in common with the Interpersonal skills proposal. Not enough to make them absolute dublicates, but there's still a lot of overlap by the look of the existing suggested questions. Should they be merged?
It would be great to see both succeed. But if one effort were to fail, it would be nice to see those users who are not on the surviving site welcomed into it somehow.
Changing the topic slightly:
If one site were established, up and running already, would the other have a chance of succeeding? I am leaning toward “Maybe not”. Would the proposers of the new site be told by other users that something like that already exists, so please do not bother? I am leaning toward “Maybe so”.
These are the thoughts that were running through my mind when I read this very good question. So I think that merging the two is an idea that has merit. Furthermore, it may be advantageous to both sites if their joined-broadened-scope were adjusted to include the concerns of the members of both sites. Perhaps the “Big Mods” already know this and are simply waiting to see what happens.