From The Standard

I see the article quotes the somewhat clumsy description of "Non-subsurface stations" so on that basis a book exchange would still be allowed at Rayners Lane for example.  Books are actually pretty hard to set light to, particularly when packed close together, so low risk at an above-ground station.  Try it some time with an unloved book! They would eventually burn if the station building went up in flames but would be a trivial part of the overall blaze rather than the cause.  One reason piles of Metro newspapers (clearly visible in one of the photos) are allowed. 

The book exchanges are not on the train where there might be rather more concern, so the (almost certainly dodgy) e-bike is very different in that respect, though modified/non-compliant ones ought to be dealt with on a wider level than just by LU as they're a safety hazard wherever they are.