[Keyframe]

True and not true. I own few telecine and film scanning machines. Most of older film material, esp. 16mm isn't worth scanning over full 2k. 1556 in y on 16mm esp. important because lots of people want to reframe into 16:9 and 1556 gives more than 1080.

Anyways, most of old stock (print, negative, ip) have grain such that over cca. 2.5k won't yield anything better. However, kodak and fuji stock from mid to late eighties definitwly is worth capturing at higher detail. Highest-detailed stock from nineties we've measured to have spatial rwsolution of around 8.5k and that's about as high as you will get (rare) out of 35mm.

tl;dr; depends on the stock

edit: Here's previous mini discussion regarding telecines, if anyone's interested https://news.ycombinator.com/item?id=11377678