They will always be an altcoin, miners have an incentive but it halves periodically and altcoin competition for miners will settle the market on PoW based currencies
But their goal is to potentially launch an attack on bitcoin, forcing the legacy chain to change the PoW hashing algorithm into something else so the attack isn't effective. This is a disaster in itself, so im not sure what we could call "real Bitcoin" anymore if we reach that point. The question is: how much money can the attackers spend on bribing miners to mine at a loss? Since Coinbase and Gemini talked about 48 hours approximately, it seems they have to spend for 2 days at least in order for Coinbase and Gemini to list B2X as BTC.