It's conceivable, but an admittedly-quick look at Regulations.gov didn't turn up anything obvious on this. Clearly, the industry is moving to 1.28 as a result of the Watersense program and certain state and local requirements (like California). Toto's line, for example, includes only a few older workhorse designs in the 1.6 gpf regime, and they are even doing pretty well with their 1.0gpf toilet.
Watersense is a good example of how the government can lead an industry to innovate and meet a new standard, rather than bludgeon it into putting out poor products on an artificial timetable, as the earlier law did. Of course, competition and innovation solved the problems created by the initial law, but consumers (including myself) wasted a lot of money on horrible products from name manufacturers that should have been ashamed of themselves for putting such crap into the marketplace in the early years.