Users have/gain the ability to create there own colour scheme/layout/icon etc, and have that as there own "Chapter" with its own name and player uploaded logo/badge.
Users that have no chapter have limited colour choice/no badge etc, and are freelance "orks" etc. When you join chapter/guild, there scheme etc is applied to your equip and a limited customisation is present.
These will be "as well as" the 'normal' chapters, Ultramarines etc...

Lots of work to get that to work, but kinda like corporations in eve, you name it, give it motto, set the parameters for whats allowed and what isn't, can charge taxation to members etc, you make your own badge and insignias/rewards for players in your group and reward them when you see fit

The devs have explained that such customazation won't be available, you will be able to customize but Blood Angels will look like Blood Angels and Dark Angels like Dark Angels etc.

Its probably a good idea they don't tbh, it will keep it proper to the 40k universe. I was just dumping brain content onto here thanks for the reply.

Np, it's cool reading all the diffrent ideas people post thanks for sharing your thoughts buddy.

Maybe you could do something similar with personalized heraldry etc, like a tabard or cape (a bit like WoW). That way you keep your chapter, but can identify clans or guilds.
Chapter creation is not really in this games purview, that's why pen and paper games like Deathwatch exist.