There probably would not be any huge issues with allowing a 50M upload.
But the point is that HTTP was never designed to handle large file transfers, becuase that is what FTP is for. FTP is great at handling files up to as large as you can store on disk, and usually a lot faster too. But in todays 'WWW' world people only know webpages. Some people still remember IRC, and that's usually it.
If you are dealing with 50M files on a regular basis, you should be using FTP rather than HTTP.
