Thanks all.

Regarding rpi4, I may not hurry to get it, because I'm using rpi
only for terminals. 1GB memory may be enough for that purpose.
However, I found rpi4 has independent ether interface from usb
(Sorry just a glance of souces), which may be better for usb itself
ether...

Do you all think to to use rpi4 for cpu/auth/file server for plan9?

Kenji