Given Gainax's history of releasing cels to the 
public (Not often, if ever), I'd say that isn't 
likely to change in the future.  In the olden 
days, before cel collecting was popular, cels 
were considered toxic waste.  You couldn't burn 
them, you couldn't sell them, so they were 
expensive to deal with (Which is how Animeigo got 
it's collection, one disposal company literally 
dumped hundreds if not more miyazaki and other 
cels in their front lawn).  I think more and more 
cels will continue to filter out, as staff leave, 
and join, or the cost of booze goes up.  I'd much 
rather see more KareKano cels, myself :)