I haven't really seen any discussion on this, but GW seems to be cracking down now on the "they're your dudes, paint them however you want" mentality with the following:
New codex, pg 177, Inheritors of the Primarch, Designer's Notes
If, in the background of our publications, your Chapter is a known successor of a specific First Founding Chapter, you must select the chapter trait of that First Founding Chapter.
This was reinforced further in the FAQ stating that Emperor's Spears have you use UM CT in this case.
How does the community feel about this? Would you enforce this in games? Especially with all the tongue-in-cheek talk now about the blue Iron Hands, this seems important to talk about.
I for one started my primaris army as Raptors in part because I know my mind wanders a lot and I like to try new stuff all the time, so who better than the Raptors to use IF Tactics one game, then RG in another, then WS in the next. I mean, they're all about using the right (lower case T) tactics in a battle. But now I technically can't (and even with the ruling on the IF infiltrator exploding 6s, I still wanted to run that list damnit!). Another successor like Blood Ravens can do it no problem. This feels like a weirdly arbitrary decision of where fluff dictates the rules in a way I don't think we've really had before.
If you use a successor with a known FF chapter, how have you been handling it? Did you even notice? Sure I could just call them <Green Bird Marines> and go hog wild, but then what if I want to use Issodon, who has <Raptors>? How are the successors restricted, while people are just painting Ferrios blue to match the rest of their, now, <Iron Hands> army?
It's been frustrating me a lot and I just want to see what other people think about it.