The ULF was the Austrian solution to providing level boarding in the typical Central European environment where (not only kerbsides but) platforms have been built over many years at kerb height - i.e. about 150 mm. It was a clever solution but the new generations of low floor trams have pretty much standardised an about 300 mm as a platform height, so that's the way it is and the ULF has become an orphan really.
But there's no reason why the ULF couldn't be ordered for a new build system I think. Do note that the ULF, execpt for the latest versions have kneeling mechanisms. The ULF has requried a complete undercarriage redesign. Do note that many modern low floor trams do have self-leveling air suspension, and at least one Flexity-Classsic-variant has (self-levelling) hydro pneumatic suspension, these could in theory kneel at stops.
Most systems with 150 mm high platforms are obviously happy to buy the 300 mm low floors and either progressively raise their platforms, or accept that a 150 mm height difference isn't that much, which it isn't for the mobile and baby buggies. Wheelchairs, representing a very small percentage of users, are accommodated by the use of extendable ramps fitted to the trams. The "Vienna" drive-over stops can also be built to 300 mm, which they are in Melbourne.
Building the drive over stops to 300 mm instead of 150 does mean either longer and/or steeper drive over ramps, see this news article.
I don't think 150 mm is that much even for manual wheelchair users, as a noted above, stairclimbing is possible in a manual wheelchair, there are electric wheelchair designs that can climb stairs, unfortuantely the iBot mobility is out of production.
Do Vienna road rules allow permissive left* and U-turns, or to only green arrows allow those? I do suppose they happily do without our hook turn, just as we now happily do without our old left turn give way rule even though now those turning right have to give way to (not get in the way of) anything that moves, and right turning drivers thus have to be aware of the eintre sutiation, with left turning drivers being ignorant of the situation as they are not requried to give way to anything, except pedestrains crossing the side street. Did you know that turing vehicles are even requried to give way to pedestrians on a red ped signal, even though pedestrians are breaking the law by crossing.
*Too bad that Mainland Europe has now standardised on driving on the right, when it comes to road vehicles, as well as trams, driving on the left appears to be more natural for right handed people, also note that most people are right eye dominant, but do note that, given that the traffic directionallity determines which turns cross the path of oncoming traffic, geogaphy and travel pattern may fovour one direction of traffic over the other.