Intel released today the Cooper Lake Xeons (4 and 8 processors versions) with the new new LGA 4189 socket (Cooper Lake & Ice Lake) that replaces the LGA 3647 socket (Skylake & Cascade Lake) used by 2019 Mac Pro.
There is even a bit of variation of LGA 4189. ( Cooper Lake is a complete non option for Macs anyway. )
"LGA4189-5, for Cooper Lake, uses PCIe 3.0. LGA4189-4, which is for Ice Lake we were told, will be PCIe 4.0
.....We've since been told that the design of the socket is meant to make sure that Ice Lake Xeon processors should not be placed in Cooper Lake systems, however Cooper Lake processors will be enabled in systems built for Ice Lake. ..."
2021 will probably bring yet another socket change for Intel's "Sapphire Rapids" follow on to these two. ( the memory I/O bus is getting substantantively wider (and faster DDR5 ) and the PCI-e is jumping to v5. both of those probably mean the inter-chip-intrapackage and interpackage fabric is also changing also. )
Even if Apple were to jump to a Ice Lake, Xeon W variant in 2021 it still would be in same position of being "last gen on that socket". Intel
AMD has a socket change lined up too.
Pretty good chance Mac Pro product line isn't going anywhere in 2020 or 2021 in CPU changes.
Ice Lake Xeon W is probably more likely a iMac Pro target. iMac Pro range core counts should be much easier to do with Icee Lake Xeon. What Apple does with the regular iMac 27" will probably set stage for whether there is a speed bump for iMac Pro ( to W-2200 series ) or jump to what is probalby W-2300 series with Ice Lake foundation and logic board change.
Later this year, Intel will release the Ice Lake processors, for up to two processors workstations and servers, these can be used by an updated Mac Pro, if Apple ever release it using Intel processors. Ice Lake supports PCIe v4.0.
Just to make it explicit, the socket change means a new motherboard. There is a decent chance Mac Pro 2019 chassis probably would not get that new motherboard. Some update adjustments to the chassis made.
All of that "change" doesn't mean a 2019 Mac Pro CPU can't get work done in 2020-2024 .