When a performer (e.g. a guitar player) performs a solo in a recording, in MusicBrainz that can be indicated by checking ‘solo’ for that artist/instrument role.
In MusicBrainz it will then show up as the artist performing ‘solo guitar’.
To me that looks funny, suggesting that ‘solo guitar’ is some instrument.
(or, you could have a composition for ‘solo guitar’, but that’s not what’s meant here)
Wouldn’t it be better if it displayed as something like: ‘guitar (solo)’?
To me, it is the “drums” argument all over again.
In “common” vernacular, we say - dude, did you hair Slash’s solo. He played the guitar solo. He’s awesome.
But in, as example, choral music, they are the solo singer, not the singer solo.
Grammatically, the contemporary use is wrong. Slash plays a guitar solo because he is the solo guitar.
Wouldn’t that be solo guitarist?
(I’m not native English, perhaps some people say he plays solo guitar?)
I guess it would be a solo guitarist if he only did solos. 
The problem is the way these sentences are built. Internally the string looks like this for all instruments:
{additional} {guest} {solo} {instrument:%|instruments}
Where the relevant instrument is inserted and whether there should be things like “additional” and “solo” in the string. So you can’t just change the order for just one instrument.
Yes, indeed, but that touches on some misunderstandings about ‘lead guitar’ and ‘rhythm guitar’ vs. guitar solo.
(and that subject is not for this specific thread)
So I understand that while this may fix things for ‘drum solo’ and ‘guitar solo’, it would also affect roles such as ‘lead guitar’ and ‘guest vocals’, and change them to something like ‘guitar (lead)’ and, vocals (guest)'.
It’s probably better not to touch this then.
(before it indeed becomes ‘membranophones’ and ‘guitar families’ all over again)
Yeah, and especially “solo membranophone’” and “solo guitar family” 
♩ “The day is ended little membranophone boy…” ♩