No, anything on "chain 1" as you put it, cannot be an altcoin.  Alternative clients are alternative clients, but until they fork the chain and that fork continues to grow alongside another fork, there is no argument about what is bitcoin and what is an altcoin, as bitcoin is the only surviving chain from the genesis block.  Any logic suggesting that changes which don't lead to two competing chains indefinitely is an altcoin is no different than logic suggesting core itself is an altcoin.  Moreover, worshipping core is like worshipping satoshi.  I'm constantly accused of being a big-blocker, but quite frankly, like most recent posts where this accusation has been flung, I'm not talking about big blocks, I'm talking about the idiocy and hypocrisy on both sides of the debate.