As soon my ordered Pi4 arrives, I intend to make a setup with CCDCiel for acquisition, PHD2 for guiding & ASTAP as local solver to test the performance of the Pi4. Even on a Pi3 with 1 GB this will work but the USB3.0 will makes a significant difference in image download speed. An USB3.0 memory stick could be used for image storage/transport and remote desktop for control over a low speed WiFi connection.
Yeah you can get blazingly fast USB flash drives these days like the SanDisk's Extreme Pro that has 400MB/s Read/Write. That's 4x faster than UHS-1 SD cards and I think that is worthwhile at about 1.5x the price per gigabyte of storage.
I myself am going to just buy the Stellarvue OS once they update it for RPi 4, probably this week or next. It has everything I enjoyed from the ASIAIR, but with way more function and customization. And I am a bit tired of overseas customer support.
My Pi 4 [4gig] comes in two days and I'll have the holiday to tinker with it. I'll probably have a 'tinker' SD card and a Stellarvue card. My first priority will be to get a powered USB hub happily working, as I only have a 12v-5v@3 amp converter and each USB3 port draws a max of 900mAh. I've read Pi's don't play well with USB power draw for gear and don't play well for finding devices through hubs.
For those of you waiting for backorder until August, or later [That's crap. Don't do that!], there are Pi4 [4gigabyte RAM versions] available if you look around.