Your STB is a small computer device so here are a couple of suggestions.
> Why not remove the hdd from your PLus box and offer cloud based storage for all of your customers recordings, Free upto 500Gb anything above that charge as a service?
>The STB runs on Linux and already has x2 USB ports, why not introduce "peripheral devices" (keyboard, mouse, webcam)
> Offer the opportunity to EU to install apps or to be able to select amonst popular apps like messanger, facebook, twitter?
> Maybe introduce a TT app store for your clients where they can "buy" these apps from your store?
Just a few thoughts.