took a look at the brommies further up in the thread, both of them are likely to have widened fork and triangle; mine are stock. the 44/305s i use are wide enough to be decent on gravel, they also work fine in snow.
btw, in snow bike geometry reveals itself. slack 'modern mtb' geometry and too much trail creates self-steering, and such a bike may hopelessly steer and skid back and forth, as the rider tries to keep the bike on a narrow track/ridge of packed snow for example after a car or people walking. its not uncommon that such a bike just comes to a stop.
the brompton is here pretty good, and even better with the smaller 305 wheels having shorter trail. it runs best if the handlebars are tilted somewhat forward, as to have the effect of a stem. this goes with the 349s as well.
have to say, one of the greater assets of the brompton in my view are the standard tires. they have decent puncture protection, and roll unreasonably well on tarmac. have used my other brommies together with friends with serious racers in 20+ mph peleton club rides, and the difference in rolling is small, not to say minimal. they go best just under 4 bar.
so i would not convert my only brommie to 305s, but having one extra for hikes in terrain or snow is perfect. an extra bike is also handy to have as a backup, or for loan to friends and family