Poly aftertouch is in MIDI 1.0 -- it just isn't used much.
What MIDI 2.0 adds per-note pitch bend. That's a big deal, but you can also accomplish the same thing without all the complexity of MIDI 2.0 by using MPE, which is an extension to MIDI 1.0.
In a way, MPE is easier to deal with than per-note pitch bend anyways. MIDI 2.0 didn't bother to extend the 7-bit note number range, so you're still stuck with 128 notes. (This despite the existence of instruments like the Tonal Plexus H-Pi, which has 205 distinct pitches per octave, each with its own separate button!) That means in MIDI 2.0 you have to pick the nearest unused note and bend from there.
In MPE it's a bit easier because you can just grab an unused channel, pick the closest note to the one you want, and bend. It's a little more straightforward, and you know you'll never have to bend more than 50 cents either way.
So far, it looks like most of the expressive and microtonal instruments out there are using MPE. The only one I know of that uses MIDI 2.0 is the Lumatone.
MIDI 2.0 has attributes in note-on messages. Attribute type 0x3 gives you 7 bits for a note in semitones and 9 bits for a fractional part of a semitone, so a resolution of around 0.2 cents.
That's effectively just per-note pitch bend -- which is great to have, but it's still kind of problematic to only have 128 unique notes you can individually toggle on and off or otherwise control on keyboards that have more than 128 keys.
It's possible to work around the 7 bit limit, but it's awkward.
What MIDI 2.0 adds per-note pitch bend. That's a big deal, but you can also accomplish the same thing without all the complexity of MIDI 2.0 by using MPE, which is an extension to MIDI 1.0.
In a way, MPE is easier to deal with than per-note pitch bend anyways. MIDI 2.0 didn't bother to extend the 7-bit note number range, so you're still stuck with 128 notes. (This despite the existence of instruments like the Tonal Plexus H-Pi, which has 205 distinct pitches per octave, each with its own separate button!) That means in MIDI 2.0 you have to pick the nearest unused note and bend from there.
In MPE it's a bit easier because you can just grab an unused channel, pick the closest note to the one you want, and bend. It's a little more straightforward, and you know you'll never have to bend more than 50 cents either way.
So far, it looks like most of the expressive and microtonal instruments out there are using MPE. The only one I know of that uses MIDI 2.0 is the Lumatone.