No way in hell should Ross switch to Black Mesa when it comes out. That would be just a dumb move. Why start the whole game with the normal graphics, and then switch to Source graphics? It ruins the flow. Also, some of the architecture of the original Half-Life can make for hilarious dialogue, like when Freeman questions why they built something the way they did.
I really don't know why some of you would want him to switch to Black Mesa. And that reminds me, if he's switches to Black Mesa, that would require him to skip through a bunch of Black Mesa just to get to the point he left off on. What if he wants to play Black Mesa from the beginning? It would ruin it for him. Not to mention for the people who haven't beaten Black Mesa, they would be seeing what the rest of the game looks like if they didn't get that far. Yeah sure, they don't have to watch it, but that's just lame.
From a production point of view, it really isn't conducive for Ross or the fans to switch to Black Mesa.