Greetings,
as a founding member of LotRO with a LTA I was ever unhappy with the vocation system.
I understand that it was introduced to encourage player interaction. I don't think this point is valid anymore, since you can bypass this simply by playing alts, which most players do.
My main argument is that some combinations are simply useless for certain chars. Example: I just started a Hobbit lore-master (thanks for making this possible btw) and would love to have him become a scholar. But when I choose this, I have to take weaponsmith which is almost useless for this char and doesn't fit to his RP background. How I would love him to become a cook instead, or maybe a tailor, or even a woodworker. Anything that would be more fitting for this specific char in my point of view.
So I would suggest you re-invent this whole vocation system. If I could have my way, I would allow free combinations of all professions. But I could also live with certain limitations, as long as you have more possible combinations. Most vocations have two professions which are tied together somehow, as scholar + farmer, tailor + forester or metalsmith + prospector. It would be a good idea to have the third profession selectable out of a pool of variants, for example historian = scholar + farmer + pick one of the following: weaponsmith, cook, woodworker.
Please think about it. Thanks for reading.