I think you’re right about the splitting thing…
Though they also propose true multichannel plugin possibility. (in addition to rats/tdm choice, which makes 4… no comment, well even if aax intend to unify that, it remains the same you have to choose between native or dsp)
Actually when you select a plugin you first have to decide if it’s multi-mono or multichannel.
Their multichannel is similar to vst3, without the possibility of target specifically certains channels, except for specify plugin like lfe filters, for instance. (So Nuendo is more flexible in this regard)
But it is true that Protools multi-mono can virtually transform regular plugins for convenient multichannel use…
That’s what is (arguably of course) “missing” in nuendo, only when different setup are necessary across channels with just one insert slot…
But the thing is, for using regularly both, I like the Nuendo style more because it’s simpler and in the end more efficient, providing you work most of your plug pre panner, meaning at the source.
True multichannel plugin come really in handy in vst3 and I find it convenient in the end to “have” to put 2+ different plugs if I want to filter differently different channels. At least, it is more clear for someone coming after me in the session.
All of that just for me of course 
Do you guys using protools and nuendo regularly have any particular other approach regarding the so called “multi-mono” thing ??