Have been interested in this since I discovered it. After Taproot the next speedy trial will probably be something AnyPrevOut related, which means closer to this becoming a reality. This idea involves what has been called "burning" coins to have a perpetual one way peg, you can't get the Bitcoin back once you enter the side chain. The advantage is no perverse incentives from additional tokens being created. What do you think?

Side note, it would be cool to see more sidechain ideas and posts on here-- I really like reading about this sort of thing even though it's really on the edge of my understand of Bitcoin.