Well, the Terrestrial Planet Finder is an actual space-based interferometry array that will fly perhaps within the next ten years. It will be able to find earth-type planets and measure their atmospheres accurately.
The TPF will use ‘nulling’ to eliminate the glare of nearby stars to detect the light reflected from the planets themselves. It will have a resolution about 100 times greater than Hubble, although I don’t think it will be enough to actually resolve the disks of planets around other stars, it will be able to make good measurements of their characteristics such as size, mass, atmosphere, temperature, rotation, etc.
After the TPF program, there are larger telescope arrays in the early planning stages. The NASA Origins program has laid out early-stage proposals for several really exciting missions:
The Life Finder is an even larger telescope array optimized for studing the atmospheres of other planets for signs of life. LF will be able to detect changing seasons, methane, temperatures, and all sorts of markers that will tell us an amazing amount about other earth-type planets around nearby stars. Life Finder should actually be able to detect large biomasses like forests and algae-rich oceans. Life Finder could be flying within 30 years.
Finally, the largest array currently on the drawing boards is the Planet Imager, a telescope array 360 kilometers in diameter, which would be theoretcially be able to resolve images of other planets about 25 x 25 pixels. This is enough to make out continents, oceans, mountain ranges, large craters, etc.
Once you’re out in space, the limits of interferometry are pretty huge. Given a large enough array, I think we should be able to image planets around other stars with the kind of resolution we have for imaging the moon from Earth.