Interesting point. This would be like moving your BTC after every BTC fork coin (bitcoin cash, bitcoin gold, bitcoin private, etc). Personally, that may be overkill. If you're concerned, you can always move your EOS before doing anything for a fork or airdrop (I covered this 9 months ago here). But you're right, if there are multiple drops, you'll endanger something (even if you move your EOS) unless you create new EOS addresses each time.
That said, I'd never EVER participate in something that required a private key. There are many other ways to do this including signed messages.
Unlike eosDAC the Evolution tokens will never be converted over to the EOS blockchain. Evolution is not a hard fork since EOS is not a fully launched blockchain.
The EVO token will be distributed as an ERC-20 token and the swap to a native EVO token on the Evolution blockchain will have no correlation to the EOS blockchain nor the private keys on the future EOS blockchain.
Way back in the early bitshares days with PTS and such, I got into the habit of changing my keys after every snapshot, and if I ever claim my balances of the Bitcoin forks I'll do the same. As long as you have good key management, it seems like good security practice. I do not like the idea of a single key controlling balances on two chains.
This is why I've still never claimed my peerplays-bitshares airdrop -- the official way to claim is to enter your BTS owner key in the peerplays client. Utter madness!