And as any rework of SW, there is danger of bugs and so on....

At that time when TotalMix was designed / invented, computers were not so powerful.
For lower CPU/GPU consumption and lag avoidance, TotalMix FX works with Bitmaps.

This makes an easy / dynamic scaling impossible. Supporting other scalings seems to be a lot of work. The currently supported scaling options try to support a wide range of screens, but due to so different resolutions and DPI values, it will not fit well for everybody.

If you look at newer implementations of RME Software (e.g. the new DIGICheck NG, RME connector) then you see that RME started using vector graphics.
But also this went not smoothly for everybody because DAW systems have been equipped with not so powerful GPUs/Graphic cards where certain minimum requirements for graphic are not met and thus need purchase of a new graphic card.

So … If TotalMix FX should support vector graphics, then
- it needs a complete rewrite of TotalMix FX, which is much work and
- some/many people would need to upgrade their DAW systems with a more modern GPU.

Do you remember how many efforts it took Steinberg with Cubase, when they introduced scaling of the GUI.
The 1st release was "so so" and it really took some time until everything went smooth and looked well again.
It think it is also not easy to get vectorgraphics done to look good and "do the right thing" if there is not enough room,
so to say if the user makes the windows smaller and smaller and possible "too small".

I am personally very glad now, that after DIGIcheck NG for Mac was followed by a Windows version
and that Auxdevice has been implemented now for 12Mic after approx 2+ years.

I think RME has this on the radar, but everything takes time and during corona plenty of resources were busy / blocked for sure having to redesign devices to handle/manage chip crisis.

I have a 2560x1600 laptopscreen and so 135% is way too small and 200% clips the screen. (Setting DPI doesn't affect size). Why not provide intermediate scaling opitons like 150%, 175%? Sure, maybe you have to do the UI for each step manually, but at least a software scaling solution with nearest neighbour scaling for example would have been at least something for those 'soft' scaling steps.