Yes, we are very busy right now, there are just so many things we can add, because the foundation that has being laid out is much more powerful than what GSX does now.
Every suggestions for an API is very welcome, but it's maybe best to wait until the product is more established in its features, we'd rather not breaking other developers work with large changes, which are still happening now.
1. Use XML LVars for the command and status interface items.
Not sure about using LVars for communication between GSX and other addons.
We don't want to have a different API for in-process (.dll/.gau) modules and out of process modules ( external .exe ) and while LVars are easy to access by dll modules and gauges, they can't from an external process, unless using something like FSUIPC is used but, since GSX doesn't require it, it wouldn't be a good idea to put it as an additional requirement for a GSX addon. On top of that, communicating only via LVariables means that to handle events, there must be some kind of polling, which is not very nice or efficient.
Simconnect, for example, provides both the ability for two FSX clients to handle custom events ( see the documentation SimConnect_MapClientEventToSimEvent, used with "Custom.event" ), and the ability to define a data area ( see SimConnect_CreateClientData ) that clients can access. Once you have events and a data area, every communication is possible, and Simconnect can provided the needed infrastructure, which can also routed on a network.
5. Allow options to suppress green-line messages and control volume of boarding sound levels.
This should probably belong to a setting in GSX itself, rather than an API that addons can call. What would happen if two GSX addons running together tried to set a different volume level, at the same time ?