Yeah, it’s great to see your commitment @jonleighton 
Yes, we wish we had a new admin UI, this item here represents the same problem, with a different solution: Backend/Admin layout overhaul
In this other post, we try to do what both spree and solidus did, revamp the existing UI in some way without having to re-write all pages.
The main problem with it, and this post here, is that, although highly desirable, this is not close to the top of our priorities right now.
This proposal here is a multi-year project and, as you correctly mention, this would require a huge amount of effort from the community in terms of Product (defining how this new app would work is a lot of work), Dev (code review and coding it in case you dont complete it), Testing and, most importantly imho, Code Maintenance (more code means more time/money goes into maintenance.
I think the main factor that makes me say “let’s not do this please” is our main constraint: lack of time, particularly dev time. Also, I think this would need to go through the normal voting process where instance managers vote in this against the other priorities.
So I try to offer alternatives:
1 - what do you think about supporting Backend/Admin layout overhaul?
2 - following up from your great idea of replacing the UI for certain user profiles: instead of replacing/improving existing functionality, what if we build extra functionality, for example, creating a new page specifically for supporting the packing process for farmers, that works on mobiles so it can be taken to the warehouse? this is just one example. (@Kirsten I follow you here but I dont think network is a good candidate because it’s a core part of the app. I think it would be very challenging to built something so core to the business model in parallel…)
3 - what if we rebuild the frontoffice and get the Mobile epic done in this manner? I’d support this mainly because it’s a task around 10 times smaller than rebuilding the admin UI.
In summary: I think starting a new huge project to rebuild the admin UI is not close enough to top priority and would be a step too big for our legs.
I think this last option “do it but in the frontoffice” can get some traction from the community mainly because it’s already a priority and I think it would make sense in terms of tech strategy: 1. to separate frontoffice from the API and 2. validate a more modern frontend tech stack (replace outdated angularJS).
I hope this helps. It’s great to have you around!