After today's announcements this is what I am looking at. The only problem I see is that current eGPUs do not support the 5k thunderbolt monitor, with exception of Blackmagic (but like most of apple products those are crazy expensive and non-upgradeable).
Until that 5k monitor situation is solved, I am stuck with iMac. I tested various 4k monitors, and somehow I find the 5k Retina (1440p) to be sweet spot for daily usage & development.
Edit: Funny thing is, if you count the $$ for above set up, you will find out it costs as much - if not more - then similar 2019 iMac. So it probably does down the the question - do you really need that top-of-the-line GPU from AMD (which isn't that fast anyway)? It seems that buying iMac that you can still sell for 50% of original price after 2-3 years and simply getting new one with specs bumped might be the same result as being able to update your ram/gpu/ssd/monitor
Seems that iMac truly is the sweat spot for most "pros" that want a desktop.