A NVMe compatible M.2 M Key connector (like the Rock 5 Model B [0] has) would have been really nice. I'm starting to accumulate old but good, yet small in storage space terms NVMe's which I'm no longer needing, but which would be perfect for a Raspi. Even if the PCIe bus were an older generation and not as performant as the NVMe.
The microSD card slot is really great to have, to get up-and-running, but once it's clear which function the board will serve, being able to move over to a directly connected old NVMe would really be a benefit, also in terms of reliability. These microSD cards scare me, yet I make full use of them.
Finally having a battery backed RTC on it is really great news.
[0] https://wiki.radxa.com/Rock5/hardware/5b