Just forcing an app update has zero effect on Apple users who turn off auto updates and android users can always roll back the app.
That will reach 95+% of their users, which is probably what they're after. The problem is supposed to be about the documented losses of power in flight, that would be fixed by a battery firmware update (and maybe FC). There have been quite a few reports of flyaways too. Both these modules are updated in the new FW.
The drone, and the app are working. How do they force us to update either one? Even with internet?
If there is a known critical problem causing crashes it would make sense to force the update - BUT it should be properly documented which isn't the case, and should be isolated from any feature updates which it also isn't.
The app will likely simply show you a popup "you must upgrade until you can fly again" and that you can't dismiss unless you've actually upgraded.
Investigations that have taken place on the firmware side don't suggest anything else can happen without app action. Of course there is the possibility that no app upgrade is needed (older app versions already have code to do the disabling), and they would just fetch the order to do so from the net if they have access.
Current firmware will happily run in September. What WAS found is that while Assistant currently offers you 300/400/500/600, once you've upgraded to 600 all others disappear, and that .600 enforces antirollback so you cannot downgrade with the current versions of known tools. BUT... that was defeated in about an hour.
Really this firmware was a first important step to know what to expect in the future, and it suggests they are trying to care for the masses but without a real desire to prevent tinkering. If they REALLY wanted to prevent rollbacks it would have been easy to do so, the way they've used is trivial to defeat.