I've been brainstorming this with colleagues at my job and tossed out the idea of including both an immediate development cost as well as a "long term cost multiplier" for every requested feature. So far, no one has the like the idea or phrase. I can't really blame them.

But there must be some quantity or term, with a nice memorable ring to it, that could get this across and at least let business people make decisions with full information at hand. Granted, any such numbers delivered in that guise would be wild guesses. But still, better than nothing.

Edit: However, I've since realized that the notion of "story points" and "velocity" already sort of provides a way to get this across if used carefully.