Will LFS track update release reset hotlaps or pb's on all tracks? Would be interesting to hear which tracks will have modifications affecting laptimes.

I also wonder if there is a reason personal best statics has not been cleared after track updates so far. For example Blackwood 2017 or Westhill more long ago.

Hotlap charts will deffinitelly be reset for the changed tracks. Otherwise you can't really compare anymore.
Considering personal best - it's up to you to delete them. In LFSW you can do that by clicking on your PB time.

We will have hotlap festival next year...

When I was just demo user, personal best reset was really easy after most recent Blackwood update. Now it will be quite more difficult after I've drove on over 200 combos.
There is an option that you can delete every personal best on lfsworld.net but I really don't want to that if no major changes happen on Blackwood or Rockingham.
Think also about airio !ex list. Deleting your pbs will greatly reduce your expercience. But that's just digression.

There is 100% chance they are deleted (remember Rockingham update was leading to OOS)... 3D kerbs are most probably not only visual ^^
And if we consider there is a chance that tire physics come aswell ...

I wouldn't mind if all times get deleted. If they still light grey like in 2007.

I prefer that before I delete them myself