A new solver was never promised.
Caustics are notoriously hard, all render engines struggle with this problem in some form or another. Many don't have it implemented at all. Knowing the time and effort it would take to create a new solver, I think the majority of the community would prefer that time to be spent on other features.
I hear you, caustics on pools is pretty much the only commercial use case for caustics right now. But the thing is, that is pretty much the only time is really needed. Would caustics add a tiny amount of realism in some scenes? yes.
Look at this examples of architecture
photography, can you find many -if any- examples of scenes that absolutely need caustics? I couldn't find examples that even show clearly visible caustics.
In your study
https://forum.corona-renderer.com/index.php?topic=30007.msg172830#msg172830 you showed a few examples on how caustics are visible in everyday life*
Except, in everyday life, no one is running around with a water bottle or hose spraying water all over the floor.
Of course you would get caustics in those scenarios... but unless you specialize in a very niche market of scenes-that-were-just-sprayed-with-water I don't see the current caustics solver holding anyone back.