I would have hoped to see the new M4 mac mini closer in design and specs to the existing Mac studio , with the Mac studio specs jacked up by a notch or two.
Base model m4 mac mini should be 16GB RAM, 512GB SSD with HDMI 2.1, with options for 32GB RAM, 1TB SSD, and 64GB RAM, 2TB SSD.
On port selection, I still feel they should retain the two existing USB-A's, add one more HDMI 2.1 specifically in the M4 pro and M4 max SKU's. They should fix the Wifi 6E 6GHz band wifi stability issues they had in the M2 mac mini. Hopefully, Wifi7 does it and improve the range of bluetooth connectivity from M2 mac mini.
I'd like to see M4 pro mac mini with a 16 core CPU, 32 core GPU.
Finally , I would like to have a feature in macOS, where I can stack multiple Mac mini's and virtualize it as pools of one or more computing storage, media, and network interface units and if required share these pools between clients/applications.