And the key point is that Wikipedia didn't have any particular outside feedback until it was already famous. Probably the first bit that really brought home that there was a real world out there was the Siegenthaler incident. Until then I think we really were flying more or less blind, while even internally the quality control was based on theoretical considerations of what an encyclopedia might look like, rather than anything the end readers were actually using it for or its effects in the world.

But what should that outside feedback have looked like? People talking about what they used Wikipedia for? I'm sure there was plenty of that on blogs. A committee of experts coming over and giving advice?

I can't really imagine what kind of "outside feedback" would have changed Wikipedia's trajectory - I don't see what would have increased the "group rationality" of Wikipedia editors that they didn't already have. Academics involved? check. People thinking hard about how to organize that thing? check. New people coming in with a new perspective? check.

Now, Wikipedia's history could have varied with some internal changes - say policies on handling disputes, on anonymous editors, a clearer vision of Wikipedia "not as a scratch pad but as the final product", etc. - but none of those seem more likely to be introduced by "outside feedback".