I love the Rig Manager but would find it even more useful if it had better search functionality:
1 - the ability to EXCLUDE results from a search as well as include them
2 - the ability to layer multiple searches to filter down to the result I am trying to find
3 - the ability to add more detailed notes
4 - drop down menus for main amp manufactures an and models as well as speaker cabinet manufactures, speaker configurations and speaker types.
5 - ability to filter and rank on gain "range" rather than actual gain number. i.e. all amps with 3 bars of gain are grouped together equally rather than gain values 3.45 and 3.46 being treated differently.
6 - ability to search on or exclude Studio or Direct profilies
Why?
Lets say I am looking for a Soldano SLO Studio profile with a Marshall 1960a Cabinet
I don't want FAS AXeFx or Line 6 Pod models of the amp but profiles of the real thing (could just as easily work the other way round the point is I only want one of those things not all of them). The ability to search for Soldano > SLO > excluding FAS > including Marshall 1960 etc would get me to the results.
The drop down pre defined menus (albeit with the ability to add custom entries) would make searching infinitely more useable. At the moment we all tag things the way we want so Meas Boogie might be MB, MeBo, Meas, Boggie, Messy Boagie....... which makes it difficult to achieve reliable searches.
Greater scope for notes. OK this is me being really OCD (sorry) but I like to know what the amp settings were including things like which channel, which mode within that channel (Boogies often have 3 or more), Bold or Spongey etc for power, which valves, valve or diode rectifier, main amp settings and GEQ settings. The same is true of mics and mic positions. There isn't nearly enough room for that.
Direct profiles are a major PITA for me in Rig Manager. At the moment I will be scrolling through a list of profiles and auditioning them. Typically I don't look at the name or details. I just tap the down arrow on my keyboard and play a bit. If it's not what I want it hit down and start again. This works great as long as ALL profiles in the sub group are EITHER Studio or Direct. I am not averse to Direct profiles in principle merely the way they rip my head off when I'm not expecting them and therefore haven't got a cabinet loaded 
Organisation features:
I would like to see the ability to store songs and set list and order/reorder these more effectively (perhaps something like the way RJM's Mastermind editor works). It would also be really helpful to manage Cabinet IR's and effects chains in Rig Manager.
I'm probably the only muppet who would find this sort of stuff useful but hey ho it's out there now 