It seems more likely the "peg" can run from a secondary protocol, that doesn't change bitcoin, but controls someone's bitcoin wallet, allowing the user, themselves, to control the peg of their assets between bridging, by the rules of the peg. I've thought this for a couple years now, but I don't have the technical knowledge to offer any sort of proposal, but the idea seems simple enough. Imagine an open source plugin for a bitcoin wallet. Perhaps it constructs all your transactions with the second layer in such a way as to require consent through this plugin to sign for future transactions using the bitcoin you put in. Maybe when you acquire goods and services on the other layer, as an example, the plugin could correspondingly relinquish control of the commensurate bitcoin from the UTXO of the bitcoin they put in. I'm just rambling at this point. Sidechains seem mostly pointless. I find side/second "layers" inevitable. "bitcoin backed currency" tell me if you haven't heard that one yet. I would rather better side layers to bitcoin than bitcoin backed fiat currencies.