Patent threats against open source have been around for more than 20 years now -- one of the first GNU utilities was "gzip" which had to use a different algorithm from the Unix "compress" program. So there are several predictable things that will probably happen if Microsoft files an actual lawsuit.

They're pretty clearly not intending to sue, since that would make it harder for them to lobby for software patents outside the US. The best case for them would be to get everyone who uses software to pay Microsoft automatically, just like everyone in the US who runs a bar that plays music pays ASCAP/BMI.