Great article. Conceptual debt makes perfect sense.
I’d suggest an interesting relationship: that technical debt is a derivative of conceptual debt
If a concept fails, then any technical debt you had in relation to it is actually a pay off — you gained time by not fully paying your technical debt.
If a concept succeeds, then your technical debt remains payable — at some point, if the concept persists you will need to pay off the tech debt, or pay some rate of interest through ‘maintenance’ overhead