Personally, I think the bloom is off the bud when it comes to space telescopes.

If you want do build something new and something cool, I would suggest a
space-based BIG EAR! Something that would let you orbit over any place on
Earth and HEAR what is happening on the ground! Or maybe three BIG EARS
in Geo-sync orbits to cover the entire planet!!!

Think Google EAR! See how seemlessly this fits in with flexible path
and Earth Space Science, and current space policy?

Now THAT'S a CHALLENGE!

;-)

Dave