For the Admin
No client to support! No admin privs required. Updates immediately. There have been reports of impressive speed improvements when running directly in the browser and not embedded in the client. Personalization appears to be much easier for users compared to the current process.
For the Developer
A lot of required epiKnowledge will certainly change. No more client DLLs. Time to replace with Typescript/Angular. Business logic must be moved to the server, where it should be anyway. Microsoft is deprecating WCF too. The loosely-coupled nature of the web will make integrations smoother. .Net 5+ is seeing impressive performance improvements over the current Framework.
For everyone
Users know how to use a browser, so the training curve might be less. It’ll be a bumpy ride and there will be growing pains, but I like the vision and I see us better off about a year from now once we wrap our heads around the new paradigm.
I honestly don’t know for sure. I’ve only seen a single page with the tree on the left but there could be some way to do that with panels. I’ll wait for someone else to chime in.