I think there are many more interesting implications of cheap-ass, automated, and decentralized manufacturing in general than just in IP. (3-d printing, downloadable and version controlled CNC instruction sets, parts supply chains on the internet, etc.) There will be lots more custom/ private work, there will be pseudo socialist challenges to the big guys who control manufacturing (in the same way that open source software is a bid to take control of software production), there will be revolutions in logistics, and we will see lots of interesting designs created outside the for-profit + mass distribution model.
There will be lots of lawyers, unfortunately.
I think we will also see the encoding of old designs first, just as Linux and BSD and GNU started as fairly traditional designs (and personally, if I were to download any car I could choose, it would be a 1977 Volvo 244).
And in 20 years, the best designs will be the open designs, just like the best software today is rapidly being defined by OSS, for many of the same reasons (i.e. no small minded MBA's getting involved in technical shit they will never be able to understand).
Amish technology will be really important in the process of shifting to open manufacturing (somewhat ironically) since their designs are complex but not crazy, and they appeal to the same DIY hippies as OSS does (I count myself in that bunch).
I also think an open source bicycle is the place to start, not a car, since it is simple but still challenging.
I think about this way too much, actually.