you mean something filesystems do as a matter of course? Ignoring resizing them which is also supported through supporting technologies I’m not talking about partitioning a drive. You can have different applications sharing a filesystem just fine, with each application growing how much space it uses naturally as usage increases or shrinks. Partitioning and namespaces are similar (namespaces are significantly more static) in that you have to make decisions about the future really early vs a normal file on a filesystem growing over time.

If you're assuming that every tenant's block device is storing a filesystem, then you're not providing your tenant a block device, you're providing your tenant a filesystem. And if you're providing them a filesystem, then you should use something like LVM for dynamic partitioning.

The point of NVMe namespaces is to partition at the block device layer. To turn one physical block device into multiple logical block devices, each with their own queues, LBA space, etc. It's for when your tenants are interacting with the block device directly. That's not a hack, that's intended functionality.