ah, that does make sense actually. but what happens if, as it becomes clear that a SC is going to win over Bitcoin, miners begin to jack their mining tx fees just b/c they can to create the SPV proof tx required to make the switch to scBTC?
Why don't miners jack txn fees today? Its actually a small "issue" in the protocol. Miners that search for a zero txn block have a tiny advantage. But miners would not want to block movement from BTC to SCBTC. It can only enhance the value of BTC since a BTC is convertible to an SCBTC at any time (and back).
Aside: This idea of a "rush" to scBTC does not make sense. People "rush" to get a better deal. But the deal will always be the same, so no need to rush.
also, there still is the question of Blockstream creating an additional asset on the winning SC ahead of time that stands to profit from a rush of BTC to scBTC.
But this "pre-mine" will be visible on the sidechain. So I suppose if you want to move your BTC to a chain that is not fully backed that is your choice. But no matter what happens you'll never be able to move more BTC back the the bitcoin blockchain than was put in because remember BTC is not actually "moved" it is "locked" on the bitcoin blockchain.
you still haven't answered how a SC can't hurt Bitcoin if the economic value of a scBTC starts exceeeding a BTC in USD terms b/c of a significant innovation.
It depends on what you mean by "hurt". Remember Peter R and how he was saying that the true value of BTC is the memory -- the blockchain history. And so he was threatening to fork any altcoin project and "pre-mine" it to exactly match the bitcoin blockchain.
Sidechains will preserve the bitcoin "memory" -- the value of the blockchain history. This will happen because you can move value on a N for M (constant) basis from the bitcoin blockchain to the sidechain, so the value ON the bitcoin blockchain will always be relevant. In contrast, a wildly successful altcoin (personally I don't think it'll happen, but if it could happen on a sidechain it could happen on an altcoin) would drain value from the bitcoin blockchain.
Yes, a wildly successful sidechain could "hurt" bitcoin in the sense that the # of transactions on the bitcoin ledger goes down (moved to the sidechain). But I don't classify this as "hurt". In fact, some would see this as an advantage. Bitcoin could hold huge value denominations of coins (1 or 2 BTC :-)) more safely than the high transaction speed, application specific side-chains. And note the bitcoin will be a popular mining destination for our lifetimes at least because of the block reward -- every BTC mined is exchangeable N for M with scBTC on the sidechain.