"Regular" size adventures (32 pages) are something that have been abandoned by Paizo. They've cut back to two-monthly 64 page adventures.
Nitpick: As I understand it, the current Pathfinder Adventures line releases a 64-page adventure roughly every
three months. At least, that's what they said when they changed the format.
I sort of expect that publishing shorter adventures just isn't economic.
That seems a reasonable supposition. Though with Pathfinder, specifically, the economics are adjusted significantly by their subscription model. (Though that suggests that if 32-pages isn't good for Paizo then it's probably
really not good for anyone else.)
However, pdf-publishing that size (either through Dungeon magazine or through dndclassics) seems possible.
Again, this is probably correct. Of course, if Dungeon remains under the DDI subscription (or is put under a Morningstar subscription or, really, is sold as a value-add* to
any subscription bundle) then they can safely produce adventures of
any length they choose.
* What I'm trying to get at here is that AFAIK most people subscribed to DDI for the tools and so got Dungeon as a 'free' add-on. I would expect much the same if it were bundled as part of the Morningstar suite - most people would subscribe for the tools and consider Dungeon a 'free' add-on. Conversely, if there was a dedicated
Dungeon subscription (or, indeed, any subscription where Dungeon was The Main Thing), then that's different - suddenly Dungeon would need to be able to do the "heavy lifting" of getting enough subscribers to be worth producing.
(And I'm not sure that's any clearer!

)