There's a difference between a toolchain becoming unsupported, and putting a hack around a feature that later becomes obsolete due to business decisions. That hack could certainly be technical debt, up until it isn't. If the code that it was implemented in is no longer used in the future, you didn't incur any cost to it.

Not an original idea but I can't remember where I heard the idea. Technical debt is the best kind of debt, because it's the only debt that you might not have to pay back.