This is highly anecdotal but the guitarists I’ve heard using it were all playing a mix of their guitar amp + some midi sounds. From what I understood, there are still a lot of misses but this is acceptable in this mix scenario.
For me this is a solution for power trios where the guitarist wants to fatten/expand his sound.
As soon as you introduce a keyboardist in the band, there will be spectrum clash… or to say it another way: the keyboardist will do better and/or add something more interesting than just following the guitar track.
I guess it could also be used by a guitarist as a pure synth instrument (without mixing the guitar sound). But then, the guitarist will face the challenge to play “real clean” and find instruments that sound good for his style. I can see this work occasionally to get some wow factor or supplement a lacking track, for a localized moment during a gig.
In a reverse way, just like when a keyboardist plays guitar sounds…
Having said that, I would not even be too much surprised if you tell me some 5-year old Chinese wunderkind has a Youtube video where he uses his guitar to play the Bach’s Toccata on full pipes 