The total surface area doesn't need to be that big, we're definitely in radio wave territory, so synthetic aperture techniques are readily usable. As long as several telescopes are more than 40km apart and have good enough clocks, we can stitch the data together to get interesting things.

I'm guessing the hurdle is most of these measurements need to be space based since all the flag ship data sets are from satellites.

if 0.07 degrees of arc goes to 50k year time scales, then 0.00007 degrees of arc goes to 50 year time scales, wavelength of 1.9 mm, rayleigh criterion of angle ~= 1.22*lambda/diameter.

I must have done something wrong because I came out to an effective diameter of only 35 meters, we've totally built radio dish networks bigger than that, heck, the EHT made such a big hubbub about planet scale scopes.