I honestly don't think we've seen the last of the 2 stroke engine in dirtbikes and ATV's. As Joe said, the clean-burn technology is already here, and I'm sure at least a few of the "botique" brands will have experimental quads and bikes out soon. Yamaha and others may be slow to jump on board, but the demand for new 2 strokes is there and I know units which meet government standards would sell well as long as their prices are kept competitive.
Direct injection is a very neat concept, and there are also other ways of making a 2-stroke engine burn cleaner than ever before.
Stihl, Inc already has a unique cutoff ('chop') saw on the market with EFI. It is extremely well-engineered, and it starts and runs better than any carbureted saw. The engine also employs an experimental technology called "delayed scavenging" to improve combustion efficiency and fuel economy. The coolest part? All this new emissions-control technology fits into the same basic package as the old-school 2-stroke engine, and the power output is the same! If Stihl can do it to a lowly power saw, others will follow and adapt the tech in other fields.