From a very quick search, I can see:
The WATE external viewfinder is US7706682BB.
The angled viewfinder attachment is US2006232858 (not granted yet).
The rangefinder 1.7x viewfinder magnifier is US6621986BB.
What looks to my unqualified eye like a class of lens designs that facilitate lens assembly is US6992845BB.
The black and white lens coding and in-camera recognition system US7848634 BB.
US publications have been cited since this is an English language forum.
Protection for the 90mm TE Macro close focus adapter has only been saught in Japan JP4486394B2 and Germany DE10354716B4 (presumably the manufacturing locations of perceived competitors in the rangefinder market).
So we can see that plenty of M9 accessories are patented. However, the actual optical rangefinder system in the M9 camera is old, so has fallen out of patent protection, as has the lens mount, obviously. The M9 digital sensor was developed by Kodak, so they probably got those rights subject to a collaboration agreement. Likewise, software development would have been outsourced, and that would not be patentable in Europe anyway (though protection is available in the US for software).
So, at first glance the answer does look to be purely economic if you can get Kodak on board for the sensor, which is by far the newest technology in the camera. But if the Leica attorneys did their job with the presumed Kodak collaboration and supply agreement, this should not actually be an option. And rightly so - shouldn't Leica benefit from the success of this product after putting all of this together when nobody else seemed to have the interest or the vision to pick up where the Epson RD left off? Good for them.
Out of interest, does anyone know a patent number for the Kodak sensor with offset microlenses? I presume they did patent it.