That's basically how discussions work in Wikipedia (and other MediaWiki projects). Discussion pages are just a giant text file which anyone can edit fully. The only extra feature over Notepad is an implicit edit history.
What made this workable was that discussions were rarely "hot" - typically you discussed with one or two users over a span of many hours / days. Once you got many people editing the discussion page at the same time, you got conflicts which were solvable but annoying.
