Snaps can use chroot. Sorry if this wasn’t clear. Snaps will also be able to privilege dropping-- it is designed and on the roadmap.
I actually think that snaps are a great technology for server applications because you don’t have to worry about all the deep desktop integration bits. You package your applications or application stack in the exact configuration you want, with the exact libraries and dependencies you want and your users will benefit from predictable, reliable upgrades (aka refreshes), rollbacks, security sandboxing, etc without having to worry about your snap breaking the system or other snaps breaking your snap (this is achieved in large part because your snap can only write to snap-specific areas).
From everything in your list (assuming you can modify your snap to use snap-specific file paths rather than writing to /var/log, /var/spool directly; but even this will be made easier with the upcoming ‘layouts’ feature that will let you control the snap’s view of its snap-specific areas (eg, $SNAP_DATA/etc/foo.conf can be accessed via /etc/foo.conf in your snap)), the only thing that isn’t supported today are non-root users and groups, and this is planned. You can choose to use classic or devmode (or strict mode and simply not drop for now) while the feature is being developed.