The limit in some sense is the size of the Earth. This picture is from an interferometer observing at very high radio frequencies (wavelength of 1.3 mm) using telescope around the Earth. To improve resolution you would either have to go to even higher frequencies (we have a very hard time doing interferometry there) or find baselines larger than what fits on Earth. And you don't just need a long baseline, but need to keep the baseline constant to within a fraction of the wavelength. So if you want to use satellites to get longer baselines you would have to know their orbit to within a tenth of a millimeter.

As an aside: that image is basically black and white. The intensity is just mapped to black -> orange -> white instead of black -> gray -> white.