I've got the Pod HD Pro and these are some things that I've noticed that would be great to have....

Automatically detect if anything is plugged into/disconnected from the FX Loop - engages/disengages FX Loop (if an FX Loop block is in that particular patch). For those that do a number of gigs and bring/leave different FX based on the location/needs. It becomes extremely tedious to go through every patch

and disable the FX Block when I dont bring any other gear)

Global Gate like on M13

Option for Global Volume - trails enabled

Dedicated, moveable FX Loop block (doesn't use a regular FX block, similar to the looper block)

Screen will change colors to match the Relay G90 color options ( I know this one is probably a  hardware request, not a firmware update)

FX footswitch assignments for FBV shortboard MKII automatically set to the type of effect (Stomp, Modulation, Delay, Reverb, Volume, Wah)

FBV Shortboard MKII ability to do Wah/Volume with built in pedal AND use an attached pedal for FX parameters (I'm unsure if this would be an FBV firmware update, hardware issue, or Pod HD update)

More amp models/FX/cabs/preamp - I know everyone requests this. I'd love to see more original Line 6 exclusive amps (clean, crunch and dirty), something that no-one else has and something that isn't a digital version of an existing amp. Eventually every company will have each made their own vesions of all the major amps out there anyway, I'd love to see something that has never been available before.

Everyone feel free to add to this post and I will add as I come across things that I see as well.... (: