Update: Our current solution for this is working pretty well. Skip to it here.
Storemapper, like many many B2B apps, allows our users to create, edit and export records in bulk using a CSV upload file. I have spent a ton of time trying to find the best method to allow the upload and asynchronous processing of very large (10,000+ rows) CSV files. This post is a documentation of our work to date on this, a plea for collective help from the internet, and hopefully will be the public home of the best solution we can come up with.