Think of your user - do you want them to type manuscripts, pages of text into the app using the roku remote? If there are common phrases, add a button for those to the keyboard to autofill/autocomplete, like for 'comcast.net' if it's an email address.
I know editing on roku with the remote is a pain, and I would do whatever I can to make the experience easier for my users... but the problem is a little different: I'm implementing ONVIF (open standard for the interface with IP cameras) in my application and what that means is that the application will pull from the camera whatever URL is used for streaming. The URL is filled in an edit box and then the user can leave as it is, or make modifications to it. The problem is that sometime this URL is very long and, with the current KeyboardDialog, there is no way for the users to even see the whole URL if it's something like this:
It would have been nice if the standard KeyboardDialog had some scrolling built in for the text...