Just throwing the idea out there...
I'll begin with the Galleries First lounge and set out the current landscape -
click here for the current layout plan
I like the Galleries First lounge. I'll expand - I like it a lot. In fact, given the choice between this lounge and Concorde Room next door, my preference is the GF lounge for no reason other than I am most comfortable when I'm left to fend for myself.
Seating:
Armchairs and ottomans are the winning formula. They work so well because they subtly define our personal space. In the old T1 F lounge, my bee-line was for the single loungers that faced the windows (not that the view there was ever particularly impressive). They were cleverly staggered and screened which added a degree of privacy. Power points were also within arm's reach. So my first wish list item would be to add a row of outward looking loungers along the south edge of the lounge.
Cathay have taken the concept of personal space a stage further with their innovative Solus Chairs, designed to provide a self contained place to relax, work and eat. Would this concept work in T5?

Cathay Pacific Solus Chair at HKIA (Flickr: pointhacks)
Terrace:
A great place to bask oneself in natural daylight and follow the apron and runway activities. The treatment of the north edge has always bothered me. From an architectural standpoint it looks unresolved to me, what with the utilitarian guard rails peeking above the parapet.

GF Terrace (Flickr: Conan Butcher)
I have always regarded this wall as an unserved stage for some theatre and nothing conveys the excitement and anticipation of international travel better than an animated solari board. Theatrics side, a solari board would be a huge improvement on the existing LCD departure boards which are, frankly, just too small to follow from the comfort of your seat.

Solari board (Flickr: Tim Schreier)
Taking this theme one step forward, let's engage in C21st technology. An alternative to the Solari board might be a full size digital animated wall. Displaying the right balance of content is a tricky one but nonetheless a perfect challenge for the nation's innovative young creatives. Off the top of my head, I quite like the idea of relaying HD video of the airport activity, neatly embellished with live data relating to each aircraft captured in frame - where it is going, and where it has flown in from etc. Perhaps some closeup live footage of ground operations (following a captain's visual inspection of his Boeing for example) would bring some small airport charm to the big airport environment. Could be pretty cool if done right.
The Champagne bar:
Located at the north-west side of the lounge, this area, the coffee house area and the space in-between appears unloved to me. Has anyone here actually chosen to sit here? No? Anyone? Me thinks this area desperately needs to be rethought, if only to improve space utilisation and reduce congestion elsewhere in the lounge. This area might be improved if it was repurposed as a relaxation zone. Add some z-bed pods complete with storage, power/data, and personal task lighting and we could be onto a winner.
My wish list isn't exhaustive by any means but I hope it serves as a discussion starter. So as you've travelled the world, are there any particular attributes of other lounges that you'd like to see at T5?