I also needed piCore for the Pi3B+ so a few months ago I put together a release and tczs that met my needs, they are available as piCorw 10.1beta1a and is available here
timjanes.uk.
I believe it is functional, has all the tcz needed to support the hardware on the pi3B+ ie WiFi, Bluetooth etc and compiletc so that it can be used as a command line development system.
I also added commands tce-load9 and tce-ab9 that can be used to load extension from piCore9, in general if they don't link with ssl or ncurses there is a good chance that they will work on this release.
It is a major amount of work to rebuild a significant number of tcz so I have only done those I need and I don't use X so I have not done anything but command line. There are reports that the basic X server from 9 do work.
I am self employed so my work load varies drastically and I have been fully occupied the last couple of months so I have not had any time to devote to piCore.
I see the priority would be to get a release that supports the Pi4 as well as other Pi and that may help to get some momentum going. I ill see if I can put a release together, I have had piCore running on the Pi4.
What are your requirements?
Tim.