Comment 7 for bug 1803203

Currently, addresses is a "sequence of scalars" (aka a list). Here is the example from the Netplan reference you quoted:

addresses: [192.168.14.2/24, "2001:1::1/64"]

This can, currently, also be written in this form (quotes optional):
addresses:
 - 192.168.14.2/24
 - "2001:1::1/64"

I actually prefer the latter form, so that's what I use today.

In YAML generally (not necessarily Netplan specifically), I think the obvious extension would be to support dictionaries in addition to scalars, for the addresses. That would allow for this type of extension:

addresses:
 - 192.168.14.2/24
 - "2001:1::1/64":
     lifetime: 0
     other: x
     future: y
     parameters: z

If you really want the flattened form, it would be:
addresses: [192.168.14.2/24, "2001:1::1/64": {lifetime: 0}]

This is a clean extension from the current syntax and supports other future parameters.

Whether Netplan's YAML parser currently supports dictionaries is another question. But this is all normal YAML. See, for example, Ansible: https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html