Is it possible to use Scaler 2 or Scaler 3 with MPE+ hardware like Linnstrument, Expressive E Osmose, Haken Continuum, Roli Seaboard, Embodme Erae Touch, etc ?
And still have the MPE stuff but in a certain scale ?
What do we lose if we use scaler program with MPE+ Hardware for fixed scale ?
Anyone knows please ?
I expect one of the devs will chip in and give your the answer from team Scaler, but the Midi Manufacturers Association have published detailed information about what happens when the world of MIDI 1 collides with the world of MIDI 2.
A key part of the upgrade spec is to make interworking transparent. This is done by something called MIDI-CI, or Capability Inquiry, where (as far as I can tell as a non-expert ignoramus) a V2 device will enquire of whatever is at the other end of the wire to figure out what to interchange. If you check at www.midi.org, and d/l document M2-101-UM called “MIDI Capability Inquiry (MIDI-CI)” (and of course you can download the MIDI 2 spec from there). These docs may answer your generic questions about hardware. Scaler, AFAIK, is MIDI 1 only.
Here’s the overall pic
Thank you Panda for your reply.
The last comment from them was in 2020 two years ago 
I wonder if for example you have Linn-instrument which is set-up in chromatic scale and you have MPE on Scaler 3.0 how will you do the portamento in a certain scale ?
You will move your finger through the chromatic scale from left to right or vice versa and the Scaler 3.0 should react how exactly ?
What setting should be used ?
Scale Notes Mapped
Scale Notes Only
Scale White Keys
Chord Note
Chord Extensions
Any developer can kindly answer ?
When can we expect Scaler 3 ?
And does any developer can comment on MPE / MPE+ implementation roadmap ?
+1 on MPE, we need it on next update 
+1 here as well. At least it would be nice it Scaler could route MPE MIDI through without loosing MPE capability.