I assume you are referring to the same limitations almost every FS on earth to date suffers from when you consume about 90% capacity?

What a useless comment. If you are running out of capacity adding disks to a zpool is incredibly mind numbingly easy.

"zfs add poolname mirror disk1 disk2"

Every filesystem has performance hit the floor when you consume all available capacity. This is not unique to ZFS but to well, reality.

No I'm talking 100% capacity, shit happens and I do t want to fight the fs when it does.

100% is a lot better than ~80% (looking at you btrfs)