I think this is a great idea. This also is something @YaniUnchained had mentioned publicly on more than one occasion. One example would be last year’s Universe 2 talk that he gave. It is a great video with many insights, I highly recommend it:
Yes, it does briefly mention spawning a HC that provides a solution to BTC, basically bringing the power of the Sophia smart contract language and FATE VM to BTC. If this is to be the AE main net or a different chain - is yet to be seen and depends on the community but it will be powered by Aeternity tech. Yani shares his thoughts in the video above with some other ideas where HCs could be highly beneficial.
If a HyperChain is a L2 solution or L1 is in my opinion a theological discussion. Since there is no locking of parent chain coins in order to execute transactions on the child chain - it is fair to say it is not L2. If one builds bridges (as you suggest), it could easily be considered L2, so it is specific to the use case and how it is being implemented.