Maybe the biggest problem with nonfolders...
When I think of it large wheels aren't really that inconvenient once the front wheels are removed and even folders with larger wheels can be pretty easy to carry around like the Airnimal Joey (with the rear wheel crammed into the front fork) or the Montague (with the front wheel strapped on), but mudguards seem to thwart these purposes because even if the wheel is removed the wheel silhouette is still there.
Is the essential feature of the folder to move the mudguard (rather than the wheel) out of the way? I personally would never ride more than a few miles without mudguards because you never know when you will find rain, pool cleaners, broken fire hydrants, etc plus when it's not raining I still need them if it was raining the day before (though less so if I'm riding slowly) and, besides, even when it's dry guardless bikes get filthy which is an inconvenience in itself for storage or multimodal usage.
Are there other solutions for blocking spray than attaching mudguards to the forks? Are there mudguards which attach solely to the wheel axle? Or how about something to knock/rub the water off the wheel before it sprays?