I'm batting on the "I hope they evolve" team. I don't have a lot of love for the Mega Evolution concept. I would rather have more Pokemon evolve before completely destroying all of their potential by stating they are at the highest evolutionary point they can attain. I don't think that Solrock and Lunatone are popular enough to get Megas, outside of the obligatory "You HAVE to do it because of the name sequence" we seem to have going on.
If they get any form of attention, either new forms for both, or evolutions for both THEN Mega Evolutions for those new evolutions.
I'd love to see both with Eclipse Form changes. Evolutions can play on the eclipse theme or even continue with the general Sun look and Moon look. I'd just prefer these before we'd get Megas of them.