"2.2 All authenticated transactional (SVOD, TVOD) channels must provide a way to sign-up, upgrade, downgrade and sign-in to an account on the device itself and not require visiting an external web page to complete these functions. (Required after March 31, 2019)"
If sign-up will be done inside Channel then I assume that the user will need also to make a purchase from inside the Channel once that sign-up is done. Are third-party payments allowed inside Channels? Is there any "credit card" keyboard built in order to be used for payments inside Channels?
If you are using Roku Billing this shouldn't be a problem. Since Roku Billing is required for certification for us everyday low-level programmers. You use the Roku account, the firmware displays anything you need, and they sign up. Then you can send what little data you want to your own server for tracking.
You would need to talk to your Roku account rep to see if you can get a waiver - they do want all apps to use Roku Billing if at all possible but some channels still use third party services with roku's explicit permission.