I'm going to take a guess that this supposed content update will be April at the earliest. Not saying they won't do some more bug fixing updates throughout March though.
9 new cars. I'll be interested to see if/how they might be spread across the 3 dealerships.
Nothing as far as I know to suggest a new track with the update. It's probably a bit too soon for them to start releasing tracks anyway, as most people are still getting used to the ones already there.
I think I heard somewhere that there were actually 50 Menu Books, and we only have access to 39 so far. A lot of them were race car related apparently. Maybe they are holding some of those back so they can offer new tracks to unlock via progression (e.g. Menu Book 40 could unlock Road Atlanta, which isn't in the game yet)
On the topic of Menu Books, I noticed that one of the tags associated with some of the GT3 cars was "Nurburgring 24 Hours". This got me thinking, if there are more Menu Books, maybe one of them is a Nurburgring 24H Winner collection featuring the M3 GT, R8 LMS '15, & AMG GT3 '16. I find it strange how the '15 R8 is 800,000 credits while the newer Evo model is the normal 450,000.