When I talk to people about getting into lightning infrastructure, i frame it as there are both operational and economic challenges.

On the operational side, you’ve got key management problems, state management problems, and then general networking. There are some unusual concerns around key and state management, but we’ll get there. Theres just a lot of engineering to do.

The economics are really challenging if you want routing to actually be profitable because routing is a race to the bottom. Its very very difficult to make money routing. More people are moving into liquidity provisioning (renting channels). Things are better there but its still hard. In these or any other liquidity services, cost of capital is a real concern because it sets your hurdle rate: how much do you have to make to generate any profit (even before the infrastructure and engineering costs, which are non-trivial if you’re handling real money).

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.