How many years is such a discovery away?
For others who are not familiar with the NASA studies, "expected" is probably too strong a word and "proposed" is probably more accurate. LUVOIR is one of four flagship mission concepts which NASA has provided with seed money. They will all be evaluated during the coming 2020 Decadal Survey of Astronomy and Astrophysics. The recommendations from that survey will then be used as guidance for NASA. So if the Decadal Survey ranks LUVOIR as a top priority (the missions are all so large that it is unlikely more than one would be funded), and if they meet their proposed timeline, then it would launch in the mid-2030s. So it's not yet a given that LUVOIR will happen (another mission could be more highly ranked), and the timeline should be taken with a grain of salt.
In fact, given the timeline, I’d be surprised if either Luvoir or HabEx, as currently envisioned, actually flies. There is a lot of technical innovation that will happen between now and then, even if the Decadal recommends one or the other.
(I work on yield modeling for the study. I make plots and animations of observations, and the times on the plot labels have disconcertingly-far-off times like 2036.)
Is such an "image" why we are discussing here?
My worry is that jwst will be too short-lived. It cannot become the fixture for decades that hubble has been.