Challenges upgrading to 64-bit version of MS Office

The volume of data (sets) within organisations is growing constantly. Most organisations already use 64-bit computers/laptops as a result.
Before long they will be forced to upgrade from 32-bit to 64-bit versions of Office as well.
However, migrating Office-applications to 64-bit can pose serious challenges if VBA is applied.

Issues with controls in MSComCtl and MSComCt2 aside, most problems will arise from the VBA Application Programming Interface (API).
API Declare statements will have to be altered as well as the used ByRef variables.
The reason is that existing API Declare statements will not compile in 64-bit VBA without using the PtrSafe attribute. Extensive rework of the VBA codebase could be the result.
This is especially true if the application needs to run on both architectures (32-bit and 64-bit). In that case additional coding will have to implement conditional compilation.

My applications are already 64-bit proof but I’ve seen a lot of applications that aren’t. Especially large (traditional) organisations use dated but crucial Office-tools that often contain separate code modules with API Declares (used for File Open/Save-dialogs for instance).

Are organisations aware of this impending challenge? What are your experiences in this regard? What tools does Microsoft provide to accomodate this type of migration?
Microsoft only seems to refer to this website of a fellow Dutch VBA developer.
Surely I am not the only one who has experience making VBA code run on 64bit Office?