You know an interesting lore-friendly mechanic would be that you pick a class (path) and if you don't pick another class after a certain time limit you're locked into that class forever. The eldar special thing could be the ablity to re-class like they change paths.
The problem with that mechanic is tactical. If you are very good at blowing shit up as one Aspect, then that is what a commander would rely on you to do in a battle. You then being forced into another role because you don't want to go Exarch would be an un-acceptable intrusion into player 'fun'.
No, it's the player's choice to even keep playing at all in the end. If you go Exarch because you like it so much (or because your group compels to to) you could attain some sort of mastery state that will give you some sort of bump in ability.
No. Going Exarch is not just about time spent. It is also about mental discipline and giving in. Eldar can spend years on an Eldar path without succumbing while others succumb quickly. A system which forces Exarch status on you after some time, is an in-accurate system and a just plain bad system.
Yeah... kinda, otherwise they wouldn't exist, might be some time or less time for each individual, but...
Thanks for the info. Why not outcasts as the default class? They have yet to choose a path and are more combat savvy than guardians.
Yes but, they aren't in the Codex so Games Workshop will be less eager to include them as they can't make as good a profit.