RE: Migrating to the Cloud
John,
This subject is not a simple one. You are correct, at this moment, there is no "clear path" from Dynamics GP to Dynamics 365 for Operations (Dynamics AX). I do not imagine this will remain the case, and likely isn't technically the case right now. Microsoft owns both products, so a customer could prevail upon them to be flexible on pricing for the migration. This is a far more logical reason for Microsoft to discount than "we want a discount please."
Given the path to product unification is clear now, I would be surprised if Microsoft and ISV's with track records in GP don't provide plumbing for migrations to Dynamics 365 (both flavors) as well.
Any other option, like implementing a competitive cloud based product, would be a basic re-implementation scenario.
Finally, there are partners that have disciplines in multiple products, and having the same partner work on both sides of an ETL project could dramatically reduce implementation costs.
I suspect things will get a whole lot clearer as things progress.