Why would they need to keep a copy of MMF2 on their machine for people to download their app/game and use/play it? Any bugs should have been fixed already with the coming release of MMF3 in mind and everything planned in advance. If you're careless and you wake up one day to find out you've been using outdated software for years, you're probably not supposed to be developing anything in the first place...
I just don't think there is any need for MMF3 to support old MMF2 files. Everything dies or gets reborn (rewritten) eventually, it'd be insane to plan with the optimism that everything you have working now will work forever.
LB, I don't think you understood my point. As an iOS App developer, I update my App's as and when needed, currently through MMF 2. If MMF 3 arrives with no backward compatibility, no way to load/import MMF 2 projects, then any and all App's made in MMF 2 will face an uncertain future for keeping them up and running. I'm not saying MMF 3 has to be able to load KnP projects, but it should be able to load in MMF 2 ones so as not to hinder commercial software developers who use the tool.