The two systems have different target markets.
Maybe, if you compare what we have had in the past they are different but that does not mean they will be going forward.
Just suppose they go down the route of a modular design comprising of stackable slabs for:
CPU
Memory
Storage
GPU
Audio
Starting at a relatively low price, say $899 you get an i3 CPU slab, Memory and Storage slabs similar to the current Mini lineup.
But wait, want good audio or a GPU, that will be another $299 for the audio slab and $599 for the GPU slab.
Want a 'Pro' setup, sure, an i9 slab, 128GB memory slab, 6TB SSD (3 slabs), Vega whatever GPU slab and so on, that will a Pro $5,999 thanks.
What's the point of the mini?
I mean speculation but what I have described has Apple written all over it and the ability to keep you locked in by purchasing new or replacing existing slabs is a winner for the bottom line.