is there a way or when will you create a way to link all of our service accounts into one universal watchlist on the Roku with automatic updates by using the service accounts were logged into?
If each Roku is linked to a different user account/email address, then no that cannot be done.
They r qll liked to the same email address!
No, that would be a form of content aggregation: Among other things, it would require you to provide all your login credentials to Roku/give them access to your individual streaming service profile/settings, or that the services would otherwise provide your watchlist to Roku, and that isnt something Roku is heavily involved in (for now/yet).
(Thats something one would expect from/for Google, which is heavily invested/involved with content aggregation on its Android TV/Google TV platform)
For now, you have to use each services built-in watchlist functionality for that, and or keep your own master watchlist somewhere/somehow.