We have idea’s in the works in the community like this one here:
these other collaterals take time and liquidity before we can roll them out. Bitcoin is low hanging fruit and won’t be the dominant collateral on Anchor (it will always be Luna). So it should be fine to roll out now, it helps us get these other ones onboard at a later date.
This old basset model is being depreciated in favor of more capital efficient liquid staking derivatives such as sAVAX, LUNAx etc where the protocol take no rewards. So BTC can be the one exception here.
Problem is that with that model in order to maintain interest pegg, without yield reserve, which would most likely be gone in this model, rates would be huge, 10%-30%, and most of people wouldn’t borrow with these rates, so rate would go even more up, since people would leave system.