Plugin downsampling
The counterpart to your new upsampling feature: How about a way to run given plugins at .5fs? Some plugins really don't like high sample rates. The TTS-1 is a good example. It screws up bad at 96kHz and won't run at all at 88.2kHz. However, if I could run it at half the sample rate, it would then be usable in an 88.2kHz project.
I'd much rather run a project at a higher rate so that everything is being oversampled (since as you note some plugins that lack internal oversampling benefit from it) and only tag the one or two plugins I have that can't handle it than fun a project at a normal sample rate and have to test and see which plugins I need to flag for oversampling.
It would be cool to just see it as a selection you can choose regardles of host sample rate: Run the plugin at 1xFs, .5xFs, or 2xFs and maybe even .25xFs and 4xFs.