It has always been and always will be about the bottom line.
That said, if Yamaha feels that it can add to it's bottom line with all things considered, they will build 2-stroke, 4-stroke, and whatever-stroke engines. Yamaha's decision to focus on building 4-stroke sleds when they did, gaining EPA credits, may prove out to be a really, really smart move. With knowing that the EPA would not be an issue, they could take their time to develop a RELIABLE, cleaner 2-stroke engine. Compared that to the other 3 sled makers rushing engines out the door just to get under EPA limits, and subsequent headaches that followed.
Now with all the EPA credits in the bank, they can introduce their new "fully tested, clean 2-stroke" to gain new customers they would have never had the opportunity to get with a 4-stoke only line-up. Yamahas are not without their problems, but IMHO they have fared better than the other 3 over the last several years and could use that to win over customer fed up with other 2-stroke makers.
IMHO, Yamaha would challenge for top market share by offering both 2-strokes and 4-strokes.
Just my .02 cents.