IS it appropriate for someone to upload/provide a link to his own performance of a piece and then ask for corrections/suggestions about matters including but not limited to basic techniques, timing, correct notes, posture, expression (of the music), phrasing, etc. ? One could provide a sheet music along with it to aid the review. If it isn't then why not? It might be very insightful for everyone.
The basic thought is that no, it won't be useful to anyone. One particular performance of yours is very, very localized and answers specific to it won't help someone at random.
Stack Exchange also requires specific problems as the basis for a question, not general requests for critique. As an example, see What can I do about my problems with piano scales which manifest in just one direction?. That issue might have shown up in a video, but it's much much better separated into a separate specific question.
My first instinct is no. They would be very hard for anyone else to find via a Google search just because of the nature of the question and likely be unhelpful if anyone did find them. They are highly specific questions. However, as far a subjectivity I think they would be great subjective questions if they got great answers (I highly recommend reading this SE blog post about subjective questions).
The other problem I foresee with them is this turning into a constant stream of low-quality, chaotic questions. We'll have a front page full of "Review Me!" questions, which will quickly become tiresome.