Saw this post this morning, but didn't have time to reply. As some have pointed out, Festool probably couldn't do much to improve the multimaster, and the compressor in a systainer has already been done by Probena.
One thing that seems quite popular is a 'lunchbox' planer. I've thought in the past that that would be a great idea, in a systainer footprint. I meant to post it at the time, but I did a concept model of it - I've just posted details in this post
Other things I'd like to see Festool make are:
a 45 degree base for the MFK700, to turn it into a small cove router;
a new version of the SE-HL Bench Unit
for the HL850 planer, with an extended, longer bed for surfacing bigger timbers (perfect for use in conjunction with the SysPlaner!);
and, I'd like Festool UK to start importing Protool, and making them properly available in the UK. They are sort-of-available, in a sneak-in-and-ask-to-see-what's-under-the-counter kind of way