That sounds likely enough - on my set when BBC4 isn't running we get CBBC (and we also get it in other channels where nothing else is happening).

What seems a bit silly is the notion that by putting on the same kind of programmes they have on BBC1 and BBC2 they would get additional viewers. For the most part what they'd achieve would be to move viewers across from BBC1 and BBC2, thus reduce viewing figures for those channels, and driving away the viewers they've currently got for BBC4. Which would mean that, even if the figures for BBC4 went up, there would be an overalll reduction in the number of people watching BBC channels.

What would make a lot more sense would be for them to try to build on the people they've got, by making it easier for potential viewers to know what's on and when.

And change that confusing name for the channel, which just increases viewing figures for Channel Four.