Preferred vs 'Space Marines' wouldn't work, as it omits SoBs, IG, Space Wolves, BA, DA, BTs, GKs etc etc. Putting all of these in makes the rule 'clunky' and unwieldy.
The Plasma Spam I have sorted, I just wanted to get that out there. lol
I would rather see the Hellions the only one with that ability.
Bear in mind they essentially get these USRs free, or at least discounted.
Also, Dark Apostles are Word Bearer only.
Chosen will be very good (think Wolf Guard or Sanguinary Guard) but quite costly too. Perhaps 'a unit of Lone Wolves' would be the closest analogy.