1. I think that would make the cooperation with celemony obsolete and if you really want autotune, I'd say just invest in it. It's good as it is, and I'd say presonus should focus on other parts.
2. Yes!!! For sure they need to put some sort of stretching algorithm like abletons texture mode too and make grain size, formant and pitch automatable. Pitch automation should then NOT snap to semitones and should rather glide freely.
3. Buffer / stutter effect would be great, but then again there a great ones out there too like the audio damage replicator I. E.
4. Hmm don't really need new ones, but rather make the existing ones completely automatable.
I. E. Make the start and end points of sampler xt automatable and maybe even be able to put an lfo / envelope on that. And also add better voice options and glide to the sampler. Make it more like a synth.