It was kind of jarring in Oblivion to have a pure melee character become the Gray Fox or the Archmage, or a mage to be the head of the Fighter's Guild.

What are your thoughts on this issue and how do you think it will be in Skyrim?

I wish for Skill requirements for the Guild, it would make the Replay Value even higher!
and it was kind of weird being Master of all Guilds, i think some guilds shouldn't have the quest to becoming master O.o

They have mentioned that the choices you make/way you play might change the radiant story but won't restrict what you can do. With that said, I do not think there will be any restrictions on joining each guild.

It makes perfect sense, which is why it's not in. Bethesda doesn't make RPGs anymore, they make action adventure games.