In gens 6-7, Scizor is guaranteed to have Bullet Punch so it can't have Choice Scarf (priority move), and Scyther will get either Choice Band or Eviolite since it is an NFE, so no worries there.u'll probably get Choice Scarf on some sets :/
Scyther can already get Choice Scarf in gen 4 (with or without U-turn), so nothing new here, and Scizor will only get it if it doesn't have Bullet Punch. I think Choice Scarf is a pretty suitable item for a 4 attacks Scizor without Bullet Punch. Unlike in later gens, Scizor is not guaranteed to have Bullet Punch in gen 4 randbats (maybe something that might want to be changed as well?).