Back in 4th Edition, we had the glory of the Chapter Traits system. So long as you balanced everything out, you could create a custom Marine Chapter that fit your taste, be it for story or competition. In 5th Edition, we had that carpet pulled out from under us, but it was replaced by the new musical chairs, HQ edition. Didn't feel like playing your Imperial Fists AS Imperial Fists? That's okay! Just use Calgar, paint him yellow, and give them a different rules set!
So far, the bonus in either of the past two editions, is that you could have your collection, model whatever you wanted according to the rules, and still use it. Who cares what color of the rainbow the figures were, so long as they were WYSIWYG, and your list was correct.
With the new 6th Edition Codex, however, and it's Chapter-specific rules, rather than character-specific ones, is this the end of the grand age of Counts-As?