I think you are thinking along exactly the right lines, just being a bit too pedantic about the terminology. there are risks and costs with “deploying” bitcoin in this way that have no analogue in tradfi, but I firmly believe “cost of capital” still applies. the proper understanding of CoC is something like “opportunity cost of alternative deployment” - you clearly have to think about that here and the risk/reward tradeoff may be new, but the principles guiding the decision are the same at a high level.