Waaaaay cool! I especially like the "upload file" option.
Three things come to mind:
1> What about an "add new file" that would put a new file up to whatever directory is currently open? Maybe from the screen just before the file-edit screen? NOTE: This could very well be a follow-on JIRA.
2> Rather than "upload file", maybe something like "Replace current file"? Just some indicator that this action will replace the currently open file. I managed to replace schema.xml with a patch file when I was testing...
3> Maybe a "reload core/collection" button so you could make the changes "live"? Whether the button says core or collection could be dependent on whether we're in SolrCloud mode or not....
Frankly, though, I don't care much if any of these suggestions is adopted immediately, they can always be follow-on JIRAs. Making this available in the UI is cool IMO!
As soon as this is committed, I'll blast a message out to the Solr list to see what people think. I think this is one of those things that people will really like.