If we assume that everyone was on board with this, you’d need to swap it on some exchange right? Cause who would be your counter-party if you swapped LUNA for BTC “inside” RenVM? So either you’d need like a Uniswap inside RenVM, or you’d need to mint on a chain like Ethereum, do the swap there, and then send back to RenVM or your address.
I don’t have an answer for you now, don’t know if either of those could be done automatically or manually or what. For now probs the easiest would be to save up enough and then send to a centralized exchange or mint on a cheap host chain and trade it.