Unet segmentation - Maximum amount of classes

Hello there,
do you guys know some good paper or a source researching how many classes should be used as max in Unet segmentation tasks? Like is there a limit when in the last 1x1 conv. layer of you you push the channels up to 1000 classes?

Or is there maybe some advice to use layers in between, to not directly increase the channels this much?

As a reminder, heres Unet: