Well the question is how many watts you need to display an error message. You made it sound like voltage was the main issue.

And yeah you're supposed to negotiate before pulling 2.4 amps at 5v but that's not usually a big deal in practice. Especially when you're actually supposed to stick to 100mA at first, but who does that.

A diagnostic LED sounds nice but given how most cables don't even have a speed printed on them good luck at something more invasive.

I will say that thunderbolt support isn't often an issue beyond the basic speed rating, and should be even less of one since USB4. And that power ratings are pretty simple, 60W or moreW. I really don't think the overloading of many different types of feature is a big deal, I think the single feature of unknown speed is the big issue-causer.