A quick trawl through the most recent four seasons of anime on Crunchyroll shows nothing I'd immediately recognize as classic portal fantasy. There are three shows that involve going through a portal into an another world, but that world is a video game (Digimon Xros Wars [an iteration of a long-running property], Hunter x Hunter [ditto], Sword Art Online).
There's one or two which are more time-travel than true portal, although the time may not be quite real history.
There are TWO, count 'em TWO anime in which historical Japanese Great Men [tm] are somehow highschool girls. THEY HAVE WRITTEN THEIR OWN AU FANFIC OF HISTORY. Never change, Japan.
It's almost an anticlimax to see the one about an elementary school boy who looks like an adult paired up with a highschool girl who looks like an elementary student or the one where a teacher starts work and discovers his students are all anthropomorphized assault rifles.
ANTHROPOMORPHIZED ASSAULT RIFLES, PEOPLE.
You can comment here or at the Dreamwidth crosspost. comments at Dreamwidth.