You're correct in that the sharp dropoff is simply because there are very few planned major telescopes operating in the UV range, whereas there are a substantial number planned in the infrared range. As I mentioned in my answer you linked to, CHARA and the EELT, two of the top planned infrared/visible projects, will use new adaptive optics technology, making them far superior to previous telescopes - even though they're ground-based.
Obviously, UV telescopes cannot be ground-based, because Earth's atmosphere blocks a substantial amount of UV radiation. Therefore, any substantial improvement in ultraviolet astronomy will require a new space-based mission. The problem is that estimates for even modest increases require much larger mirrors. Proponents of the Advanced Technology Large-Aperture Space Telescope (ATLAST) proposals say that an 8-meter telescope, at the least, is needed to get good results at 0.11- to 2.5- $\mu$m wavelengths. That's much larger than HST or JWST - and ATLAST could grow to 16 meters!
If ATLAST or a similar project is pursued, the angular resolution at UV wavelengths could be on the order of 0.1 arcseconds or, hopefully, lower. That would match and then beat Hubble. But early estimates put the cost at $4.5 billion for the 8-m version, and Hubble and other space-based telescopes have been famously hurt by unforeseen cost increases. Smaller strides may be needed before we can get to 8 meters, and certainly before we can get anywhere near 16. That's going to take a while, probably a decade or more from now.
###References
