Saying 1/3 of your requirements is already done in GPS Recorder is not a true statement...
This is a design issue : wanting to keep a GPS track from a day of hiking or an hour of motorcycle racing is absolutely not the same thing.
For hiking, you may want to keep position every 5 seconds or even minutes just to keep some waypoints here and there, but for racing, you may indeed want to record as much data as possible to have a consistent track data and even to gather some stats from it.
No matter what you say, this is just not the same purpose.

May I add that hardware and software of the Nokia's Nxx series was absolutely not designed for this 'realtime' purpose ?
If I strictly follow your state of mind, you may want higher GPS precision, so just don't rely on the TI GPS chip embedded into the N900 for example.
I also would not rely on the current software side because this is just not like reading a raw NMEA feed directly from the GPS chip and modifying an internal state while reading it...

I get your point about muxing needed data to get everything in a single stream.
This is indeed as easy as reading X,Y,Z data from a device and output it to a stream, but again : this is not the purpose of GPS Recorder !

I hope you will understand that all those realtime/telemetry features you are asking for are just out of topic.
Maybe this is because I was not clear enough in my description, or maybe this is because you did not take time to actually try the application I share before posting your 'requirements'.