We have functional jobs which enumerate lists and spawn parallel stages for each item in the list. We have several which run 100+ tests.
The load speed and page width of the built-in job status/summary screen scales really poorly with the number of stages. The page width is ugly after just 10 stages, and the performance becomes a problem around 50 (depending on the resource of the machine). Over 300, it can become unusable and can crash browser, especially when multiple tabs are open. The blue-ocean plugin is certainly better, but it's still a problem with the official jenkins UI, so i'm reporting it.
From a UI perspective, I'm sure there are a number of simple ways to resolve these two issues without an overhaul of the whole page, and without breaking backward compatibility. I will suggest one, it may be a terrible one, but my org really wants these problems to be fixed.
Add a section in Manage Jenkins somewhere for global GUI setting defaults. I'm surprised nothing like this exists already. Add "max stages" setting in that section. Have the job status/summary page check that setting, and only load that many stages while rendering the page. Add a "show all stages" button to that page when rendering pages which exceeded this max.
Also of note, I am going to open another ticket about default view rendering of the pipeline_steps view which also scales very poorly when nesting many jenkins functions. I think this could also benefit from having a number of relevant settings in a new "global gui setting defaults" section.