[tehbeard]

HTTP/1 requests (uploads in this case) are also separate to some degree (though there are fairly stringent limits on connections per domain iirc which HTTP/2 resolves via the mentioned streams/multiplexing of connections).

The problem they have specifically would be that in a single request (form post for example) those uploads will be linear.

Solution really boils down to paralellizing the upload, using protocols/standards like https://tus.io/ or S3-compatible APIs to push the data up then syncronize with a record/document on the server.