Hi,
I figured that training during the off-season for the drivers is the same training we have between two races.
As we have more or less (depending on the league settings) time of off-season, it should be useful to implement an off-season training where the driver could improve more than during the season.
We can compare with real-life racing, where off-season stands between november and february/march, and grand-prix about once in 3 weeks (average).
In that new functionnality, we could select one or two axis of development for the drivers, and get the normal value for training if we select two axis, or the double value if we select only one.
To be fair, i was just speaking about driver training, team training would be another story :)