For those interested; after a ton of work revising things and accounting for a lot of the initial feedback here and from folks directly relaying info, there is a newly minted version of this pitch here.
The pitch shifted a touch more towards transactional based changes (since we feel that is more appropriate for observation) and refined a lot of the naming to more clearly indicate both the utility of specific APIs and fall more in-line with other existing APIs. The SwiftUI part is pretty much unchanged from the initial pitch here. In addition we have some initial versions posted as a pull request which is nearly ready for merging.
We think we are really close to a great solution here and would like to drive it forward with yall's help and feedback.