What should you do now? When you are ready, turn this functionality on for existing apps and update formulas and controls as needed. Most apps will not require any changes. The biggest source of changes will be for the use of Option sets and Two option data types as described below.
There is no pressure to do this as the old functionality will remain in place for a while and we only changed the default for new apps. But eventually we will be deprecating the old functionality and your existing apps will need to be moved forward. You can start to do this migration now.
The concern is listed in red above. When we turned this setting on in one of our main apps, we received over 650 errors in the app checker. While most of the fixes are quick and fix other errors downstream, not all are quick fixes, as detailed in the documentation.
My question is: when do you plan on turning this setting on? We have deadlines and other functionality to work on. Could you point us to a clear release schedule/ timeline for things like this?