I would love to see more Pottermore content.
Pottermore compatible accessories and hair styles. My Pottermore clothes look so good outside Pottermore, because I can dress them up a little with accessories and less uncanny-valley-ish hair styles. Surely that can be possible within Pottermore with the addition of some jewelry and better hair implementations that are still in keeping with the spirit of the place.
The Leaky Cauldron would be a welcome addition to Diagon Alley.
A Hogsmeade area including the Three Broomsticks, the Hog's Head, Shrieking Shack, and any number of other shops and storefronts would be fun to explore.
A house-elf personal space companion/appliance wandering around doing menial tasks here and there, or even just carrying a tray of food and drink, would be a worthy addition to a Potter-themed personal space.
@pheonixgate1 made excellent quidditch-related suggestions up-thread. I concur! Indeed it was a missed opportunity, not creating a set of quidditch world cup items to coincide with both the football world cup and the quidditch work cup coverage in the Daily Prophet over the last several weeks.
Expand the LMO series to include sitting position emotes, poses, and action.
Different than the standing avatar assuming a sitting position, these would provide functionality to avatars that are using a seat, either baked into a space, of furniture item with the sitting position.
A todo, for SCEA/SCEE the avatars fall backward through the seat when using the local chat channel while sitting,. this has existed for as long as I can remember, it would be a good time to revisit that unwanted behavior, and correct it. ... please.