Reports (or maybe just rumors) are starting up about stadiums getting done in Oakland & SD. If the Rams become the 'only' team in L.A., I would bet the NFL will use the vacant "2nd Team" slot as on going leverage for other stadiums to get built.
San Diego may be viable, but I'm not so sure about Oakland, they're in a tougher situation economically. The question is how much of the Chargers bottom line is hurt by the Rams AND the Raiders moving to LA? Spanos is correct in worrying about his cash flow would take a hit, but I'm not sure that splitting the city with either of the two teams would be good for him, he's likely playing second fiddle to them both. Obviously being a tenant vs co-owner hurts a little more as well, I'm not sure how much Kroenke is willing to negotiate there, but if Spanos were to pitch in, it could help, if they were the teams to split. The Chargers best move for their overall dollar is likely a split with the Rams in LA, or Rams in LA and them in SD, and the Raiders in St Louis.
I heard/read (not sure which one, I don't remember) recently that the Raiders wouldn't mind a rebranding, which a move to LA doesn't help that. Not sure if St Louis even helps that to be honest, they may be stuck with the image.
Either way, I think SD can probably make something happen, if Spanos really does want to stay (similar to Kroenke), but I'm not sure about Oakland. Their best option is probably what St Louis has, assuming Rams leave. Cheapest for them, but gives them a good base of fans to grow, likely gives them the most profits.