I don't think they'll announce another spin off, it just seems highly unlikely since the one they've been discussing hasn't even been released yet. If Pokémon Smash does decide to announce the spin off that we already know about, well, I don't think I'd be that surprised.
Though no matter how much we try and guess the possible date for a third game it's all left in the mystery and we just have to wait. Though if Pokémon Smash doesn't bring up a third game OR remakes, I'd say we'd probably get something like that later on, could be months or another year. If RS remakes are announced instead, I'd probably bet Gray wouldn't come until next year.
Though no matter how much we try and guess the possible date for a third game it's all left in the mystery and we just have to wait. Though if Pokémon Smash doesn't bring up a third game OR remakes, I'd say we'd probably get something like that later on, could be months or another year. If RS remakes are announced instead, I'd probably bet Gray wouldn't come until next year.