the sentence

[NewHope]

Could you explain the definitions of "downside" and "popular" below?

Context:
the only downside at present is that fashion cloth could prove too popular


(1) Downside = A disadvantageous aspect?
(2) Popular = Widely liked or appreciated?

If so, please explain why the talker said "could prove too popular"?

[Francois]

You're right. I suppose you mean fashionable clothing, or couture collections.

FRC

[NewHope]

Thanks Francois,

Please give an example to explain why the talker wanted to complain being "too popular". Usually, we know the more popular a thing is, the more advantageous the thing will have.