Hi
So running a dietpi off a sdcard is problematic… you get wear and tear on sdcard, you get the slow sdcard read-write rate (and if you bump that up you lose the wifi), and any buffering back and forth.
Is it feasible to get a dietpi to run off a ramdisk on a RPi3 or even a Odroid C2 or XU4 ?
It depends on what you are doing. Writes are the issue with SD cards and eventually even with SSDs.
This is why DietPi I do believe has log files to RAM as option to prevent wear and bloat.
The XU4’s I use daily (not an expert with them). They have USB external connector - which you can connect and external drive to (spinning drive). The XU4 in a Cloudshell/Cloudshell 2 will add more drive ability. The HC-1 gives you one 2.5 inch drive as option.
With DietPi you can move your install over to the spinning drive (built in feature).
I’ve been using SD card solutions for 5+ years and haven’t had a bad SD card yet. However using these for limited writes - not using them as download boxes or anything and logs are always turned way down.
Hope that helps and gives you some ideas.