I never have seen the used ram over 1GB. I doubt you can reach 2GB of used ram with current zynthian software, not matter what sound fonts you load or plugins you use.
Perhaps the most ramnivore element is the audio player, and if we improve the use of zynthian as sample/loop player, certainly more ram will be used. Anyway, 4GB is a very decent amount for almost any use-case.
Current 32bit image can’t use ram over 4GB but the 64bit zynthian version will be available before Christmas, allowing access to any amount of memory you can buy. If your use-case is so memory hungry, you could buy the 8GB version and wait a little bit for the 64 bit version. IMHO, most real use cases for zynthian will keep ram usage under 1GB, so you would pay for ram you will never use.
Simply for checking my words, could some of you send a screenshot of the webconf dashboard while using your zynthian very hard? Try to use as much ram as you can for a real use-case.
Regards