So, I did find a way to generate Ansible's inventory dynamically from TOSCA.
What's interesting about my solution is that it requires nothing specific on the TOSCA side, no special types and no metadata. Instead, you have a "tosca.yaml" file used by the plugin to filter the node and/or capability types that you want to consider as "hosts". This means it can work with any TOSCA profile for any environment. What's left to do is mapping properties or attributes to required Ansible host configurations.
What's also interesting about this use case is that it does require a universal way to refer to types. That's where Puccini's "canonical type names" come into play, where I use the double-colon to specify the unambiguous names, e.g. "tosca::Container" ("tosca" here being not a user-specifed import namespace but the universal profile name). We've argued before over whether TOSCA should specify a canonical type name format, and I would say this is a good example of where it would be beneficial to have a standard.