Thanks a lot everyone for the answers.
I was not aware, that nanite turns assets into imposters when they get smaller than 12x12 pixels.
However, that is not a solution at all for the problem.
If we assume fullHD, that would be equivalent to a screen size of 0.011.
If we assume 4k, that is a screensize of 0.0055.
But there is a lot of assets at screen sizes in the range of 0.2 to 0.011(or 0.055).
These assets would often benefit hugely from not being rendered with a masked blend mode.
Hence a way to switch out the material or the material blend mode, at a certain distance, would be extremely helpful for optimisation of open world levels. Especially those that feature lots of masked materials.