I think that depends on how you view characters who cast rituals. Is a character who started out as a Fighter, then trained in Arcana and learned to cast Rituals still a "Fighter" in his own eyes and the eyes of the other characters or is he something else? In my opinion, a character who trains in an area that is normally outside his specific "career" and then gains magic powers related to that knowledge has transcended he boundaries of his original class and become "wizard-like" or "cleric-like" enough to count as a member of those groups, even if the sum of his abilities isn't exactly the same as a normal member of that class. In fact, if your point of view is that being capable of "extreme feats" that alter the very fabric of the world through magic is the defining feature of a Wizard (or Cleric) then that's even further justification for considering anyone who acquires that power to be part of that group. From that perspective, rituals are still only available to Wizards and Clerics, some of those character just come to be Wizards and Clerics through non-standard routes.
That is a good way look at it.
I overall honestly dont like the general direction of it for my own version of a FRPG, but at the same time I think that your idea is definitely a great way to approach 4E. it does not do much for the wizard unleashing potent powers during a battle but it does address some of the other issues in a nice manner.
It does render the class names somewhat irrelevant

Basically it means that Wizards (class) just practiced combat magic while everyone (generally i believe most everyone would) practices magic.