This is very left of field idea, and probably not something that could be implemented in the HH3 without a nearly complete re-design, so I am not expecting it to be implemented - but if you ever make the HH4, I would love this feature:
Separate a show file into two sections - a "Venue" file and a "Show" file. For example, at the moment, I have a number of show files for the venue I work in - one for each current production show, and one for "Other" stuff - they all have some common elements - the base venue patch, base fixture presets, base venue cue lists (house lights, non dims, work lights, bingo etc), but they also have massive differences between them as well - additional fixtures patched, cue lists and chases for each show etc. Now the issue comes when I need to go from "Show A" to "Show B", or when I need to borrow something from another list, or we need to change something like the patching (having to recreate the same thing on each show file). There is also the fact that the "Other" show is a huge beast of a show with 150 odd pages of shows, with no easy way to find out if a show has been done before and some cue lists have been recreated so often it is not funny.
So my idea would be to split a show file into two sections - the venue section includes house patch, basic pallets, common cue lists etc - the bare bones - preferably marked read-only, requiring an 'administrator' to alter it. The second section is the show section. It contains it's own pallets, groups and patch and is additive. The only thing it overwrites is the patch when there are conflicts (show file only contains extra fixtures, not the whole house patch) and fader assignments. So when you start up the desk, it prompts you to load the venue. By default it opens with a blank show. You can then load in as many shows as you require for that session on the desk (from a nice, tree-structured show picker) - so I could load "Welcome Aboard", "Mark James the Juggler", "Generic Comedian" for my welcome aboard show - and with some carefull planning when programming,my 4 welcome aboard cue lists would load onto faders 1->4, my juggler to faders 5 & 6 and my generic comedian wash to faders 7 & 8. Faders 9&10 would have house lights and a house ballyhoo and my wing would have some more "every day house objects" on the last 5 faders as well, all on page 1 (because that is how I 'designed' the shows to interlace)
It is a concept sort of thing which I think if properly developed and researched would make the desk so much better for the corporate and theatre markets - maybe not as useful for the rental market though.
Or - a very simple thing which would be great too - some form of "Cue list sorter" - with the ability to put cue lists into folders and search.