When installing Office 365 ProPlus today, the recommended and default architecture is 64-bit. It has been so for some time, but it’s not until lately (at time of writing) that the Office Deployment Tool (in short ODT), is able to migrate from 32-bit to 64-bit in a single operation.
I have tested the migration, both using Microsoft Intune and System Center Configuration Manager and the outcome is what made this blog post.
Note: Migrating Office 365 ProPlus like this, from 32-bit to 64-bit in production, probably has more to it in terms of considering third party add-ins. You will have to test and make sure those add-ins are compatible with the relevant 64-bit Office application. I expect there will be some migration paths for those as well, where you will need to remove the 32-bit add-in prior to migrating Office 365 ProPlus to 64-bit.