11s is possible on a standard 9-10s hub with Shimano XT M8000 components.

And for road 11s, the difference in size of the cassette is very small and won't cause problems with a 130mm spacing (all 11s road bikes with rim brakes have a 130mm spacing).

Now about the choice between upgrading the existing bike or buying a new bike with 11s, actually there are very few folding bikes with 11s and they are high end = expensive.