With +4/-0 votes on my question and no comments or answers to the contrary, I've gone ahead and created the solar-system-evolution tag. I've added 14 questions so far, and about once a week I'll add another group as I did here though I won't make a blow-by-blow list this time because this one seems more straightforward.
This will join the other evolutionary question tags:
I've added the following usage guidance:
Questions about the long term evolution of solar systems. For other questions about solar systems use the solar-system tag, for questions about star, galaxy or planet evolution use the stellar-evolution, galactic-evolution and planetary-formation tags.
I'm not yet sure what should be done about: