More like "altcoin airdrop", as all Bitcoin owners will get a new altcoin for free, if it will actually survive the chain split. But as for USD value, it's not unlikely that even combined price of BTC + new altcoin will be below current price for some time. And it's hard to say what would be in an alternative scenario with no fork planned, because current price to some extent was formed by news and plans to improve Bitcoin in the near future.