We have successfully upgraded our 100 Full clients from 32bit to 64bit. One major pain point was copying custom credentials between registry hives. I first needed to backup the 32bit registry settings to a different location, then restore the 3 "MultiPwdMgmtIDs" keys using Powershell.
We also have around 500 Host installations, and around 5000 QuickSupport installations. I recently rolled out a new version of Host and Quicksupport inside my company, to bring all installations up-to-date. On this page (32-bit or 64-bit client - TeamViewer Support) from June it says 64bit upgrades are "coming soon". Do you have any timeframe for this?