- How stable is VST Live today for real live performances?
Stable enough to have it as a respectable member of Steinberg family.
- Would you trust it on stage for backing tracks and MIDI control?
I use it right this way - backing tracks, recorded backvocals, MIDI (including virtual instruments) and live vocals. I don’t use DMX yet.
I had few live performances last year with version 2 and this year with version 3. Last summer, in the hot sun, the laptop and audio device overheated, but VST Live, like a spaceship, did its job perfectly. 
- Have the major stability issues from earlier versions been resolved?
Yes. In 2024, some situations made me doubt – is it possible for me to go on stage at all? But last year I realize in rehearsal that a hour or two I can run smoothy my setlist in one go, where are bunch of fx plugins in every song and have no problems at all. If everything is properly prepared, then nothing can stop it.
- Does it generally behave reliably nowadays?
Yes.
- And does its functions work as it should?
For me - yes. During the preparation phase, there may be situations where you feel it needs to be implemented differently to provide you with greater comfort. But if you add your intellect, you’ll find many workarounds to get to the target. In the rehearsal process VST Live is like a playground - you try this, try that and can achieve the goal differently. Once prepared, your setlist is like rock - will play also after thousand years 
Bugs, like any software, are there. The nice thing is that the team is working on them every week. I’m sure that VST Live alone is very close to perfection. Then comes 3rd party plugins, individual needs and workflows. All this adds millions of colors to the palette.
Today, I don’t know of anything that would stop me from going on stage with VST Live 2 or 3. Both versions (latest builds) are good. I prefer v3.0.33 (ouch, while I wrote this short message, they released 3.0.34 - it’s time to install and test!!!)
Seriously, I’ve been waiting for software like this for almost 30 years so I can get everything ready for the stage.
My laptop - Ryzen 5 / 2 GHz (very old from 2019
)
Audio - UR44C
Synth, also used as MIDI keyb - Yamaha CS1x
Additional keyboard - M-Audio Oxygen25
Virtuals - essentials from NI Komplete 14, Steinberg’s Absolute 6
FX - stock, Waves Audio and NI.