In the case of permanent import, there will be contentions on which network the real BTC lives on. If Zcash were to be successful, it’ll do so in a multi-chain world. In this multi-chain world, different communities will stake claim on which network the “real BTC” lives on. Won’t the value of “BTC” then be fractured among zBTC, xBTC, pBTC, wBTC and other alphanumericBTCs? There will be cost to importing ledger to other chain.
Also, there is always probability that BTC will survive on its chain. If Zcash were to be so awesome and we can support billions of users, what prevents BTC core devs from forking the tech and import the ledger where ZEC is replaced by BTC on the new “Shielded Bitcoin Network”? I would imagine something similar will likely happen and I prefer that the chain BTC survives on is Zcash.
“In the year 2100 the whales notice that the mining reward is basically zero, and there are fewer and fewer transactions happening on the slow, expensive, zero-privacy BTC network. So they decide to simplify and save money by shutting it down.” (Gavin Andresen in A Possible BTC Future)
What I think would be worrying is for a new community to launch their tokens as ZSA and use Zcash network as their main home-ground as freeloaders. My intuition says that requiring ZEC to pay for transactions would be enough to prevent the freeloaders problem in Zcash. However, would that stay true in the long term?
Personally, I would prefer if minting ZSA requires paying fee which will be collected to the dev fund. This way people who wants to develop on Zcash will contribute to the fund that has enabled them to do what they want to do on Zcash.
Edit: clarification on freeloaders problem.