Take the activity information, time and distance and user info, sex and age. Calculate and profile the Runner:
- vo2max
- vVO2max
- Coopertest

Profile:
The profile tables are available online so it will be easy to profile according to the calculation, for all of the 3 values.

History Profile:
Take averages and make the graph of all 3 values.

Trainning plan:
Suggest interval training to increase the vo2max and vVO2max according to running data.

All formulas are free and available and easy to implement.

Average pace chart should be based on the same custom ranges you specify for the predictions in "Settings".

not all of my run keeper runs go onto the calendar, why?

Import training programs from RunKeeper

It would be great if I could add interval (both time and distance based) to my run, and then have that appear in runkeeper on the day of the run or even as a one off exercise.

You could use daily forcasts to recommend the best time of day to run. Weather apps have by the hour what the temp is predicted to by as well as precipitation. You could use that data to tell the user about certain times of the day that would not be recommended to run due to high heat, rain, or snow.

Since I can hardly consider my current pace "running", I show it as "walking" in Runkeeper. That data is being ignored but would be useful for me in developing my next training.

In most training programs you don't want to increase weekly distance more than 10% per week. A plot of total distance would help keep track of that. Adding an overlay of %change per week would be even more helpful.