Despite being a cyclist myself (Hi ED and TC ) I can't really see the point in providing it at the football, or any other major venue in all honesty for the very reason you've outlined above. Cycling through Arsenal traffic after 5's is a nightmare. It's a nice idea, but won't work. They should have reduced the car parking further though on the basis that they should have organised suitable public transport. 1,300 spaces is a lot for a society that is trying to dissuade people from driving.
Edit: and the colonnade should be interesting, I hope they don't have to fill that all up with fencing / gates. PVC wrap (similar to the Olympic stadium which worked very well) looks good.
With regards to the proposal itself, hard to see much about it and those corners have potential to be quite bland, but the general masterplan seems logical. Am I the only one that seems surprised that they haven't allowed for a proper indoor facility - multi use space doesn't count? A few folk on fezbook questioned why it's on 20K, I think the figure is bang on given the amount of games we actually get anywhere near that figure. Better than having a soulless bowl.