David Alcock sounds an important note:
All of that is very good however a word of warning has been issued from the MSSQL Tiger Team if you are using SP1 on the “lower” version:”you might see some unforeseen errors or databases might even be left in suspect state after uninstallation of SQL Server 2016 SP1. Even worse would be if the system databases are using new features for example, partitioned table in master database, it can lead to SQL Server instance unable to start after uninstalling SQL Server 2016 SP1″.
This makes sense: if you’re using new functionality and try to revert back to a version without that functionality available, there could be an issue. David links to a test script you can use to see if your database is using any new features.