I think they will start adding more serious adult flicks to October after the success of Gravity, Captain Phillips, and Argo.
Certain months and times I think will stay similar to how they are. The Summer will always be a blockbuster prime spot because so many people are on vacations, kids are out of school, etc. It's the same for Winter holidays, when people are out of school and work they are more likely to go see a movie. That doesn't mean they won't, but not in the rush factor numbers that happen for a lot of summer movies.
If you want to release a tentpole in a non-summer/holiday month you need the right movie during the right period of time. October isn't a great time for young adult/kids movies because of school being so fresh off the bat and all of the friday night football games, unless it's a horror movie near Halloween, but it's a prime spot for adult entertainment, you just need a good movie that can garner some legs. (So many examples of adult movies working with leggy runs in September/October. It's a great place to put some Oscar contenders)
January is typically a bad month because people are trying to get back into the schedule of work and school post break, but with Oscar nominations it works for that, plus MLK weekend has proven to be a good time to release movies.
Early February has also proven to be a good spot because of Valentine's day weekend, movie's are a popular date choice.
March and April are good for Spring Break and Easter Holidays, because of the staggered nature of these though it allows for a good number of early tentpoles, but they aren't strong enough to sustain a lot.
When it comes down to it though, even if you can get some hits in April or October it doesn't mean those months can sustain lots of tentpoles like June or July. Studios need to be careful when placing movies in these months, they can support a couple big hits, but that doesn't mean they are prime months to release your tentpoles (especially risky ones).