For Apple is no complication...they are just derivations...you cant have the same architecture as you have in an 13" ipad pro/iphone as you do in an mac pro.
Can't you?
Bloomberg says the ASi Mac Pro will have up to 40 CPU cores and up to 128 GPU cores. If you take four "M1X", each with 10 CPU cores and 32 GPU cores, and interconnect them, you have 40 CPU cores and 128 GPU cores. Take two, and you have the other Mac Pro configuration Bloomberg noted: 20 CPU cores and 64 GPU cores. And Apple has evidently been working on just such an interconnect for multiple M-series SoCs.
If Apple feels that ECC memory is a requirement for the ASi Mac Pro, they can add that support into the memory controller and use ECC DIMMs. If they feel the ASi Mac Pro needs 8 USB4/TB4 ports, they can add the additional controllers to support it.
This is really no different than how Intel does things. A W-2100 Xeon is the same as a Skylake-X Core i9. The differences are in the supporting chipsets. In the case of Apple Silicon, the "supporting chipset" is part of the main die.