The history of the WSM has been...very little change.
- 1981: 14.5" and 18.5" WSMs are introduced.
- ~ 1983: 14.5" WSM is discontinued.
- ~ 1983: Switch to aluminum legs and access door. (Steel legs and access door tended to rust.)
- 2000: Switch from wooden lid handle to plastic lid handle.
- 2009: 22.5" WSM is introduced with new features: lid thermometer, redesigned access door handle, and tabs that allow access door to hang open. These features were added to the 18.5" WSM at the same time.
- 2014: 14.5" WSM is reintroduced with a new feature: silicone thermometer grommet. This feature was added to the 18.5" and 22.5" WSMs at the same time.
That's it!
I am with TimA in that I would not be surprised if Weber did something crazy like a limited edition colorful WSM, but I have no insight into if or when this will actually happen.
Given the tendency for smart cooking devices in the SmokeFire pellet grills and now in Genesis Smart gas grills, I can also imagine incorporating such a device into a rolling cart into which the WSM is placed. I don't know how big of a seller that would be, but probably not enough to make it worth Weber's investment.