It would be easy mark this small zero page as beeing part of what really should have been a huge zero page. (One way would be to have two small zero pages, the old one and a new special one that is only used as a substitute for the huge zero page.)
My thinking is that this unintialized memory is not really read much until the first write so it is not performance critical. That assumption may of course be wrong. Btw, what programs are reading unintialized memory and why?
But on the other hand, if there is a lot of reading of this zeroed memory, wouldn't a single small page fit better in the cache, thus improving preformance?