I'm not sure the Tetris-like shapes are distinctive enough with no other branding, but I very much like the concept.
This is why I think it would be best to limit the silhouettes to certain situations, but I think the flexibility of having the different versions allows for varied usage.
I'd prefer it if the numeral font were closer to Gill Sans than the one you've selected.
Did you think about making the position of the lower box relate directly to the number of the channel? Perhaps 1 could be underneath the first B, 3 under the C and 4 could be below and right of the C?
I didn't go for Gill Sans because the number 1 looks too thin with this design (and I didn't have access to the old-style numerals to see if that would improve things)
I didn't go for placing the numerals in that way because having the "4" hanging off the end would be unbalanced in comparison to the other logos, and would mean alignment issues. The current positions does however relate to their numbers in a less obvious way...
I think the concept has legs, but I feel I'd need to see how it work on screen on things like idents, end credit promotions and menu boards and also if the concept could be extended to non-numerical brands like CBBC and the BBC News channel. I don't want to give it a grade yet as I don't feel I've seen enough.
I always think the classic BBC '2' symbol should be used instead of what you're using for that logo at the moment.
Personally, I wouldn't extend the concept to CBBC or CBeebies. The separate branding used for the whole lives of the channels has worked well, and I feel smothering those brands would be a poor choice.
BBC News could potentially be incorporated - I'll see what I could do with it if I carry on. I may give examples of ECPs
and endboards or whatever if I continue.
I didn't use the classic "2" symbol simply because it's rather limiting in terms of matching. It would be a bold move to drop it, but it would be easier to do it now the "2" is in an ebb.