@sam thanks for the words of caution here, as I am just about to embark on this project.
I was encouraged to see the discourse hub seems to already do this - why do you anticipate such a high cost? I was imagining you just need to get the webview and authentication working, then notifications is a nice to have. This would be an awesome feature to add into my already existing app, my team has done webviews previously.
Is there something I am not anticipating that will cause a lot of work / updates?