It's fairly trivial to build an entire OS into an initramfs to run from memory. Also, the poor performance of most microSD cards is primarily due to their flash quality, and designed use case in phones and cameras for external storage. Using a quality thumb drive or SSD over USB 3.0 would yield substantially better performance.

The OS uses free RAM as a cache for file reads anyway. Temporary directories that are not meant to persist after reboots are often mounted as a ramdisk however.

I've gone for an SSD over USB3, and get good performance - though RAMdisk would certainly be faster still and feasible with 8GB.

Running from RAM would also be great for having an effectively static system -- just reboot to get a clean slate; the hardware storage needn't even be available after boot.

IIRC this is the default mode of operation on the Alpine Linux version for the Pi.