Just to make sure all accounts do support Suitescript 2.1 already. The only thing people can enable is that 2.x is always using 2.1 instead of the legacy 2.0 runtime? Or is there still a user setting/feature Netsuite needs to turn on to support 2.1 scripts?

2.1 has been supported for a little while now. It is a very good idea to be explicit in your scripts between 2.0 and 2.1 in the header, and not let the system/account settings pick