Hi Martin,
No progress on that for the moment. Even changes that seem to be small can require a lot of development effort: between planning, implementing, testing,…I would suggest that you add your suggestion with a link to this post to the Desktop feature requests post: https://community.pix4d.com/t/3951
I might have an alternative method that could help you mark your images faster. This method is easier when you have two screens, but also feasible otherwise. The sidebar for marking MTPs can be detached by clicking in the top right as shown here:
Then, the Selection section can be folded and the window can be enlarged, as below:
This makes a lot of images visible at the same time and makes it easy to mark images in a fast manner.
Hope it helps!