I've been reviewing a lot here and at the links and I don't know if anyone has suggested this. I have not seen it anywhere yet. If it's already been discussed, sorry.
I don't know if everyone is assuming this is a permanent reunion, but this Van Hagar thing may not be permanent. It is possible that it is just a one last time thing for the fans, and a good way to promote a new compilation CD. It is possible they will go their separate ways after the summer tour of the North. That would help explain whey there was no formal announcement. They don't want to answer a lot of questions, they just want to make music.
And if this is the case, it is also possible they may do the same thing with Dave - a brief tour in the South starting in the fall or maybe early next year. Again, just a one last time thing for the fans. I don't want to get anyone's hopes up, especially mine, but it is a possibility. Maybe they just went with Sammy first because he was available. Or maybe they know that after Dave no one would want to see them with Sammy.
But even if they don't tour with Dave, after this, they will probably go with someone new, and unknown. They tried that before with Mitch Malloy but they screwed it up by making everyone think Dave was back. Then Mitch said he wouldn't join them because he new everyone would hate him.
From their point of view it does not make sense to pick Sammy or Dave because, personal conflicts aside, with either one they will have to give up half their music. It makes more sense from their point of view to leave them in the past and go with someone new who will sing both new songs and all the older stuff. As musicians they don't want to give up half their music, and the only solution is to get someone new.
I personally, would prefer to have Dave back and I think that would be best for the fans (most of us anyway) and I think they would make better music, but they seem to think the singer shouldn't matter.
Just one possibility...