Since Volumio runs on SD cards, it would be a good idea to use JFFS en.wikipedia.org/wiki/JFFS, at least for the partition with the system, using ext4 only for the boot partition. If both can be JFFS, even better.
Is there any plan to switch filesystem in the next releases?
I investigated such possibility, the problem is that bootloaders (u-boot) are designed only to work with ext type partitions…
Maybe the Pi is the only system that could run on different fs, but I have to investigate it further…
I checked right now and u-boot supports UBIFS, that would be the best alternative if you decide to change from ext4: UBIFS has on-the fly compression (two different levels of compressione) and is meant for NAND devices, such as memory cards, with wear leveling and bad block tracking.
en.wikipedia.org/wiki/UBIFS
en.wikipedia.org/wiki/Das_U-Boot
Of course the final decision is up to you 
Interesting!!! Really! I’ll work on that and update you soon on that
I suggest using the highest compression while you install the packages and prepare the system, then, before dumping the system to a file for distribution, switch to the lighter compression: most of the space is saved on the packages that you install and that will be only read and never touched, while the subsequent writes (logs, user data, music database…) will benefit from a faster and lighter compression, since they are smaller anyway ad the benefit of an higher compression would be negligible anyway.