There has been a lot of discussion about this in the past, and the sort-of consensus was (or at least the decision by OSRF) that from a development and maintenance perspective and a fear of breaking ROS1 for ppl currently using it, the only option was a clean slate (see also the end of Why ROS 2.0?).
Perhaps at a high level we could seek conceptual re-use / transitioning and a shim could help, but not sure whether what you’re suggesting is practical (personally I’d like it too though).