This seems to somewhat confirm my thinking that the skill system in Numenera reflects the originally design intentions behind DNDnext.Haha I don’t have an NDA - all this stuff is publicly available in the playtest packets, though they are a bit tricky to find these days.
Fundamentally, skills worked the same way they do now throughout the playtest. That is to say, if you had proficiency in a skill, you could add a bonus to ability checks to resolve actions to which that skill might be beneficial. The specific bonus changed from draft to draft. They started out as a flat +3, later changed to proficiency die (which still exists as a variant rule in the 5e DMG), and finally to the proficiency bonus as we see it in 5e. At first though, there was no list. You just got a number of skills and you could pick whatever you wanted. Want a bonus on checks to run, climb, and jump? Use one of your proficiencies on “Athletics.” Want a bonus on checks to weave baskets underwater? Use one of your proficiencies on “underwater basket weaving.” With no fixed list, you could be proficient in anything you could describe in a few words.
Of course, players wanted a list they could pick from, so we got a list pretty quickly. And the exact form of the list changed a few times as WotC tried to find the degree of specificity that satisfied the greatest number of players. But you can see vestiges of the no skill list approach in other optional skill variants in the DMG. Background proficiency is probably the closest of these to how it worked without the list, and though I’ve yet to run a campaign with it, I find it a pretty appealing variant rule.
It would be a better game if they'd kept it. The playtesters are not always right.