would agree once, however all craftworlds seem to have one now, based on a lot on the new fluff direction. Though I would assume Biel-Tan would take to the field with theirs more often.
But it is a great deal easier to add Chapter-specific units in Eternal Crusade than it is to add Eldar-Craftworld-specific ones. For example, the super-heavy Void Spinner - a full blown Engine of Vaul! Seeing those en-masse wouldn't make any sense. Seeing several Sanguinary priests from the Blood Angels or Iron Priests from the Space Wolves is possible, however. And then there is the example of Alaiatoc - a Craftworld, which DOES have a speciality (that being Rangers) but would go against the gameplay the devs want for the game, hence them not having that specific class.
I wonder if when they talk about squad composition they can make changes based on craftworld. Perhaps more aspects in some way for Biel Tan. Some of the earlier info indicated the main aspects will be represented. Could include an aspect that is not for Biel Tan since it is the craftworld with the highest concentration of Aspect Shrines. FWIW
Has anyone ever heard of the slicing orbs of zanthros aspect? There's some fluff and a whole lot of speculation because the aspect was never fully developed, but you can find some info on Google, lexicannum and warseer very small aspect from a very small craftworld that kicks very much ass!!
Actually in most cases Craftworlds don't have extremely unique units. yeah, you're not seeing Exarch council outside Biel-tan Or Black guardians outside Ulthwe Or all-bike warhosts outside Saim-hann But, alas, Aspect warriors are the same. I once tried to create a separate "homebrew" supplement to Eldar codex. Biel-tan, Saim-Hann, Yll-kaith... But people are obsessed with tourneys and mad restrictions. It was a failure.
Well, rangers are outcasts from different craftworlds. They don't belong to any craftworld. But Alaitoc is the one that deals/utilizes their services the most. So as much as I'd like to see rangers (and 95% of the time I use them in my rosters), I understand if they aren't included.
Every eldar unite is unic in its way, both the way they deal on the battlefield, and in the cultular way, for exapel Banshe and the Dark Reapers, total diffrent from each other in every way. There for craftworld should have uniq units. It should be diffrent in the statiscis in the name of unit and skills. if the SM have it all the other races should have it allso.
To use your example with Alaiatoc, their speciality is no more outstanding than the black guards of Ulthwe, Wild riders (note now all jetbikes are referred to as wild riders), Iyanden wraith guard etc. there is nothing special about them at all, just they are found in more abundance on a particular craftworld. Everyone has rangers and pathfinders, just not as many or known, Which could in some way be a sign how crap the Alaiatoc are if they a spotted all the time . Marine chapters differ, you won't find Death Company outside the BA + successors. Eldar lack units that are truly unique to said craftworld. the only way you could come even close would be to have under the Eldar Race banner, Dark Eldar, Craftworld Eldar, Corsair Fleets and Exodites. But that won't happen.
Shadow Spector Aspect, Eagle Pilot Aspect, Crystal Dragons Aspect, Slicing Orbs Of Zandros Aspect. Also not every Aspect has a shrine on every Craftworld. I don't think the Slicing Orbs have an Aspect anywhere except Zandros. I'm not even sure if Iyanden has a Banshee shrine currently present. Many shrines are left and forgotten waiting for a new Exarch. A Craftworld could easily go through a time with a missing Aspect Warrior set.