Either way you'd still have to code in a new feature. For both you'd just be creating a transactional database of change events. The way these events are synchronized to other possible clients is no matter as it would (or rather, should) be a completely different system. It really wouldn't be all that complex to implement assuming you're doing it (the real time editing) as a team and thus connect to one another explicitly rather than hooking the game to get the clients which you need to sync with.
You could easily use a tunneling system to virtualize a LAN setup and ease connecting to one another without worrying about real-world IPs, etc.
TBQH, having to upload to a site or send-file would be more troublesome, at least on the end user. Even if the uploads are automated, the clients would still have to download those files. Even if you automate that, you'd have to figure out a way of notifying those cllients (has to be networked some how, even if it's on the site...and you don't want to be constantly polling a file on a webtsite do you?) and after that's all said and done it'd end up being more complex than a simple network client connections which send small amounts of info (or entire databases if they're joining mid-game editing). Not all (if any) of those IM clients have interfaces to automate send-file operations either. On top of that, you'd be limiting the end-user to a specific IM client that you only choose to support when ALL end-users will have a network connection if they're wanting to do networked real-time editing.
How about we give some thought into these kinds of things before shutting them down