On his blog, Mircea Popescu claims the old chain will have an advantage:
The situation here is aggravated by the fact that the fork proposed is not simply nondeterministic behaviour, and so the holdings on the two chains aren't notionally equivalent. Instead, all the holdings on the Bitcoin chain are accepted as valid on both Bitcoin and Gavincoin, but holdings on Gavincoin are rejected by Bitcoin. Consequently, everyone involved with the fork is writing options to everyone in Bitcoin, free of charge.
He makes similar claims here:
mircea_popescu: ben_vulpes if one block's large and the other small, all i need a tx that's included in the large block but not the small one. then doublespend it on the small one, which will be rejected necessarily by the large block blockchain.
mircea_popescu: now i have bitcoin separated in two addresses, one for each chain.
mircea_popescu: the attempt may fail, but the cost to me of this failure is not significant, so i can keep on trying until it succeeds.
mircea_popescu: the only way to guard against it is, obviously,for the ."large" chain to maintain 1:1 identity with the "small" one. because you don't just fork bitcoin.,
ben_vulpes: i still fail to see how you're going to make a txn that gets included in the large block chain and not the small block chain.
artifexd: ben_vulpes: You don't. You keep sending money to yourself until it happens.
mircea_popescu: ben_vulpes what do you mean ? it necessarily will occur.
mircea_popescu: since one contains more txn than the other by definition.
mircea_popescu: suppose i make 50k 1btc txn. they don't fit in a 1mn block. they do fit in a 10mb block. what now ?
I'm skeptical of these claims -- but how exactly is he wrong?