Well I have no idea when the first vacuum appeared with a PN or brush roll on/off on an upright. This is due to the UK's lack of interest in cylinder vacs with PN heads, sadly and, also for the fact that in the UK, upright vacuums in the 1980's and 1990's were slow to have the brush on/off control, again no doubt separating buyers between the upright V cylinder debate. I do have a Sebo K3 with likewise PN head but I seldom use it, preferring the more traditional way of using suction only floor heads. 

However, I also have an old Felix upright - it has that similar PN that Sebo kit out for the K series models in the U.S and it has a brush stop roll button. It is far easier to use that existing feature than physically swapping floor heads over and for some brands, PN heads are different from one another. In terms of Sebo's ones for example I seldom have a need for the bare floor tools just using the PN brush roll on/off function. The only time I use the bare floor tool alone is if hard floors really need a good clean with large clumps of dirt like loose papers etc that could easily clog the PN when the brush roll isn't moving as opposed to light surface dirt that the PN can handle with the brush roll switched off. 

The U.S have been lucky to get Panasonic's upright vacuums that have the brush on/off feature under the Miele Powerhouse range. Our UK versions of Panasonic's upright stopped having the brush roll on/off feature as it may well have affected sales of their cylinders/canisters.

The first vacuum I came across with that feature was my moms old turbomaster. good machine that was cleaned up lots of illegitimate party's when my parents were away hehe

I wish the X1 would switch off - its an issue that all the X's suffer from - constantly rolling when the handle is put into the upright position. The Felix and Dart switch off but only the Felix's hose has a safety stop, stopping the brush roll if the hose is taken out. I never understood why Sebo can't fit an auto stop function on the X models. I'm told it was because Sebo want the X to be as simple and efficient as possible, which was another response given when I asked if a variable suction dial like the one on the Felix would ever be fitted.

Sensotronic - I share your opinion about the little circular stop button - but I give it a hefty push and it usually works first time - if you tap it gently, it won't function and I think Sebo did that intentionally as a fail safe. I don't think the stop button should be fitted to the handle though - bear in mind the Felix & Dart are both sold with the Deluxe Kombi suction head as opposed to the ET-1 and it would probably cost the company more to put a stop button on the handle, then having to blank it out for those models without the power nozzle.

As for the ET-H, I think Sebo UK will eventually change to the ET-1 floor head, but then again they seem to be happy to churn out the old ET-H floor head for the K3's. The ET-H is a bit smaller, more compact and not as tall, making it perfect for the K models.

I tried mine with the Felix since as you know I'm not keen on the cylinder set up and it was ok but like you, I didn't feel as if the brush roll was touching the carpet that much and it lacks an upright lock action since it is only made for the canisters/cylinders, thus won't allow the Felix to stand up on its own and liable to fall at the sides.  As you know the ET-H has two brush rolls similar to the X5 upright et al - it also feels a great deal heavier than the ET-1 even though it looks and feels smaller - it is after all much older by default and I like the simpler single roller brush bar release for cleaning than having to faff about with two smaller brush rolls. 

sebo fan , the reason that sebo has a brush stop feature on the felix is its two motor design, its a simple switch that needs fitting, on a single motor design you would need a clutch system like the dyson dc04,07,14 models had. what is interesting is that the x models already have a clutch and gear system inside them so it would just be a mater of making it manual operated with a knob. it could be done, heck if you are handy and enjoy building things you could build it on yourself

I was just going to say, the X already has a clutch- but isn't that for compensating for the extra turbo brush added to the hose, as the X1's shut off compared to the later X models? Also there's the double thermal cut out feature to consider - which the Felix doesn't have.