Pressing * on a Roku remote did enable record now (toggle on/off) in the Live TV screen years ago.
I was much distressed when it stopped functioning that way.
If you use other OTT products on the Roku that use the roku video player you might find that this is the standard menu that the video player uses to enable/disale CC.
So I don’t think it’s as extendable as you think
So it was there before?!!? Did they replace that to put on “cc” turn on/off?
Conceptually pushing the “*” to bring up sub menus is very easy. One can have not just the turning on and off of captions but a record now button.
Could it be that while in the roku video player you can have the * handled by the player as CC or passed onto the channel - tablo app.
If it’s passed on then the tablo roku app has to figure out how to turn CC on/off. So if the * is passed onto the tablo app how does the tablo app get the roku video player to turn CC on/off seamlessly.
The Tablo record now feature was disabled after Roku enabled their own * feature.
That’s a good point. Rather than going through all the details of what is possible with existing Roku remote control, if Roku just added one more button (future model) to have it as an “APP” customizable button, that would allow flexibility to solve this and maybr other issues. I would be willing to buy a new Roku remote (not too $$) just to have the record now feature. 
Also to select on replay only feature I like very much.
Currently Roku has 4 useless buttons – well, unless you subscribe to those 4 specific services. The chances Roku would add a button for anyone to use, with out paying them for some customization function, even though the possibility may exists, is most likely wishful thinking 
3 Likes
Adding a button to a remote is probably cheap compare to the cost to change their UI, app framework, and SDK.
Not entirely useless. I set up an automation that looks for those apps to be opened on my Roku TV. The automation then redirects the Roku TV to the app I want.