Expansion probably wouldn't lower the cap right away, as teams would probably pull a Winnipeg and require some kind of longer commitment. It will likely inflate it artificially initially, allowing teams to do stupid things, then stagnate or decrease.
How many markets realistically would be in the top half of revenue?
Seattle - maybe, but probably not. Can be wishy/washy about their sports up there.
KC - I can't see it happening here, already failed twice. Another Atlanta
Markham - probably the best bet, but based on CDN
Quebec City - another potentially solid place, but again based on CDN
Vegas - very risky, poor economic climate
Once the shiny new toy phase its over it's going to be another drag on the league. What would help the cap most is to contract, but we know that's not going to happen. Expansion would be boom or bust of the Kings. They could lose a big contract, but if they didn't it could worsen the cap issue.