The Chargers and the Raiders are in the same division so they would basically have 10 home games a season. I don’t see the rest of the owners in the NFL much less their division being comfortable with an advantage like that.
9 home games, in that one of the Chargers-Raiders games already counts as a home game. While there may be an advantage in having a little less travelling, this may be off-set in that in both of the games with the stadium mate, one would effectively not have a home field advantage.