Hello our lord,Scawen.
I was thinking of what Mandula was describing in his post (https://www.lfs.net/forum/post/2013145#post2013145), but will try to describe it:
how it works: see the livestream of Mandula (https://www.youtube.com/watch?v=riOnLRULzR4&t=5429s), in which at the top you can see two red/green deltas (SPEED DIFF/ TIME DIFF), one for speed (could be useful too), one for time difference. Basically, a realtime +/- delta time shown, which compares current rolling time to a past personal best lap at the same spatial point on the same car/track combo. That way, a slightly earlier braking point or a much wider-than-optimal turn taken (compared to the PB lap) would instantly show up on the delta (it would go from for example -0.080 to +0.110, preferably from green to red font). If a lap finishes with a better laptime than that previous PB lap (so delta is in -negative when crossing finish line), now that lap is saved and becomes the comparison reference in the next lap. I am not sure about the programming side of things but I guess somehow saving the driven path with a time value for each spatial point on the track, then while driving comparing these points would work. And if a better lap is driven, this PB path/time "object" is overwritten. This could be saved locally somehow (at least that is how Lazy does it), so if there are two races on FBM/SO4R on two different days, on the second race it is already comparing to the previous known PB lap. Could be integrated into LFSW too, since it already tracks online PB times. Not sure if it could be easily integrated.
where it should be displayed: I think once there is a reference PB lap to compare to, should appear in the top right corner under the split time.