I agree with you, these two very close wheel sizes is a stupidity.

But its like that and the problem is that ETRTO349 was a Brompton size still mainly used on the Brompton which is limited to about 37mm tire width (it seems that 40mm would fit on the T-line?), so with the exception of the 40x349 Greenspeed Scorcher (and Tru Blu), there are no tires wider than 37mm in ETRTO349.

In ETRTO355, there are wide tires (ETRTO355 is also a BMX wheel size), and the Birdy is factory equipped with 50x355 tires that fits with mudguards installed (the Birdy Rohloff is factory equipped with mudguards and Big Apple 50x355).

There is another folding bike with a folding rack for full size rear pannier + Brompton compatible front block: the Vellobike but the rack must be manually folded (which easily done without any tools). But its folds bigger than the Birdy.