A simple feature I would like to see with S3D is a change in colour of the parts of model that are actually touching the print bed before a process is applied when viewed from the bottom.
I like the ability to 'air print' with S3D as there are some specific uses for that, but there have been a handful of times where I haven't realised the model isn't actually touching the bed when it's gone to start a print and wondered what on earth was going on.
I have a FlashForge printer which I use FlashPrint for and part of my pre-slicing check is to have a quick visual under the bed to see if and how much of my model is actually in contact with the bed. This also helps with determining setting print bed temps, whether I need a brim etc etc.
I've added some photos to illustrate. In one of the bottom photos I've lifted the highlighted model by 1mm and you can hardly see any difference in the view unless you check side on. One way to be sure that all the models are definitely on the bed is to 'drop to bed' just before you process, but that then also changes the arrangement.