I mean, it's a tradeoff. It will always be a tradeoff, so the answer you're going to get is "never". There will always be less cores vs higher base clock (i'd imagine).
However, the clock speeds of ryzen/tr/epyc/whatever are more than enough for a "good" workload. In fact you could argue that unless you're doing something which requires only one single core (and honestly, I can't envisage a workload like this in a professional environment, but i'm surely wrong) the speed is fantastic and not really noticeable.
It's incredibly easy these days, at least in .NET, to parallelize workloads locally, so using something like this would outshine any 4ghz base 8 core any day of the week. But to actually answer your question as to when can we see 4ghz+ base clocks on 16/32 core processors...the next 5 years? I guess...
Yep and the bottleneck moves around as well, Intellij used to take an age to do a full index rebuild on large multi-language projects, on the Ryzen 1700 I have it pegs all the cores at 100% for a few seconds and is done, the bottleneck now seems to be back on the disk access.
I pigz'd a 5GB archive in <20s and the bottleneck there was the SSD again, (Samsung evo 850 but it was a lot of small files and ~60,000 PDF's (don't ask...)).
The Ryzen 1700 paired with a good SSD is a dream for development workloads.
If the other cores aren't doing useful work they'll be powered down to let the remaining core run faster. Not perfectly but the extra millimeters of surface contact with the cooler the extra cores provide probably makes them a net benefit in that case.
