I checked with Cotic and Paul gave the following reply, which I hope he won’t mind me repeating here:
“We’ve really enjoyed riding the 27.5+ wheels on our Solaris bikes. We have two pairs of wheels, one with KOMi25 rims and one with Scrapers, both fitted with the Trailblazer 2.8 tyres and they fit fine in the frame.
Obviously the narrower rims are lighter and the wider rim give the tyre more support, but both are a riot to ride and don’t really feel any heavier except for the initial pedal stroke when setting off.”
I reckon KOMi25 on the back and Scraper on the front would work well, although the tricky bit seems to be finding Trailblazer tyres in stock anywhere.