I'm not sure I understand. The customisation the dev's will give us won't be over the entire armour. We will still look like an Eldar of one of the available craftworlds even if we decide to customise a forearm armour piece and make it bright pink.
I mean that, each Craftworld has a unique quality that makes it what it is. Biel-Tan has masses of Vehicles... Alaitoc has masses of Rangers... Ulthwe has warlocks and farseers out the wazoo... Iyanden are ga known for the use of Spiritseers to guide their Wraithlords and Wraithguards... i'm talking outside of the obvious colour schemes. You... You wouldn't really use pink, right buddy?
Blood-red would be more my thing. That's a fair point about each craftworlds flavour. Problem is, nothing is unique to any of the craftworlds that's likely to be included so you can't apply restrictions. One of those things we'll have to ignore I'm thinking.
Perhaps we could see some of the common strengths of each Craftworld regardless? Maybe the majority of Vehicles are supplied by Biel-Tan? What if most NPC psykers are Ulthwe... Alaitoc Rangers are the majority of guards around bases? Just for the extra Immersion i think, and it'd be a decent way for players to learn some lore visually, without having to read text.
If we restrict this to NPC's then this is a great idea, assuming this is sound lore-wise. Player characters should keep their choice for practical reasons as well as the fact that there's no iron-clad reason for limiting units. Vehicles being from a variety of factions would be fine I think. Biel-Tan are more known for their glut of aspect warriors, not vehicles specifically..as far as I know.
I'd like to see multiple burning craftworlds. All the colors of the rainbow. But in all seriousness they will probably only use one.
Well, at least this isn't like the choices Space Marines or Chaos must make... Chaos have a few Legion specific units ( Along with their need to represent a favourite Chaos God )... and the Marines might like Imperial Fists, or something not an available choice. Eldar have the most popular Craftworld's listed ( excluding Saim-Hann )... i'd say more of the other Armies Favourites will be left out, at first. Hope the Ork's get Goffs klan... Thrakka fans would be disappointed otherwise.
Mayebe someday there will be a game about Eldars only where 1 specyfic units = eldarcraft worls, ho knows ;] but not in the EC