I wonder if it can be detected by the streaming apps. Some of them are really anal about ensuring you can’t record or whatever, and don’t work if it doesn’t get all the HDMI security stuff just right.

If I’m understanding what Roku has done, this has nothing to do with HDMI (HDCP) security. Roku is inserting the ads after the signals has left the HDMI subsystem, and before an image is displayed on the screen. They can do this because the Roku is inside the TV.