I know about hammer-on samples (and not arbitrary ones - it's a specific interval) but I'm not aware of pull-off ones. However, assuming you have such a sample from somewhere - you'd have that sample's Waveform loaded into an element and then set the XA Control to Assign 1 or Assign 2. Under the element's "Osc/Tune" menu, set "XA Control" to "A.SW1 ON" or "A.SW2 ON" depending on what you want. And elsewhere you can set the assignable switch to momentary or latch (under Common/Audio section which is global for the entire Performance).

More detail is in this tutorial:

https://www.yamahasynth.com/learn/assignable-switches-1-2-mastering-modx

think I've figured out a way to do this, with an "another/other" Part being the "MONO/legato/portamento" triggered pull off sound, when the key is lifted above another that's held lower, and AssignSwitch on. Will experiment and let you know how it goes.

Wanting this to be dynamically playable, not baked into a sample.

Not the same but as a guitarist as well, I've wished glissando as offered by the DX7 was implemented to handle slides between any 2 notes which would play all the chromatic notes between. Also useful for other instruments. With newer advances, the speed of the glissando could be adjusted by mod wheel or aftertouch or ribbon or ... Not velocity without other changes although I wish velocity could be a source somehow. Maybe just a rate modifier for glissando.

The samples are limited and I've also wished for more manual expression for guitars. I play single note guitar a lot not in the band but for "fun".

Strumming is something that I wish was easier too. Like being able to assign 2 keys as "low" and "high" and if you press the low key first followed by the high key, it "strums" low to high at the rate according to the time between these two strum triggers. And would strum high to low if you press the high trigger key first before the low. The 2nd strum key you press could dictate the velocity or elect to do velocity based on 1st on. And that holding down the first strum trigger while pressing the 2nd (low first held then high or vice versa) would work similarly but allow just pressing the 2nd trigger together and letting go to strum back and forth. And letting go of the initial held note would stop the next strum. So you could stop in any direction.

There's a lot of things that can be explored not possible without changes to facilitate manual realism where currently ARPs are the best way to achieve this. With caveats of lack of dynamic (not loud soft, but vs. static) control.

I've put the glissando idea up on Ideascale already. Some of the other stuff and even further ideas I've just not asked thinking I'd have to roll my own MIDI controller solution to get traction.

Last, I'm aware of 2 zone strumming although I'd prefer economy of strum control rather than having every finger responsible for the string to string delay (sweep speed). And aware of note off back and forth strumming which has the issue of being difficult to either force ending on a downstrokes or repeating two downstrokes. Assuming note on is a downstroke.

Wow. You have thought this through, and then some.

Strongly agree with all you're saying.

It's more of a pity because the MODX/Montage are so very good at guitar/strings/plucks/bows, and sax, brass and clarinets, where much of this would be great, too.

On a different note, spent today making a push 5 keys, walk away/evolver. Probably infinite variation due to using primes for many of the LFO rates. A real; "Look, Mom, no hands!"

Will have to find a way to share these things.