You will be very successful with a lot of class combinations ... when you are geared.

If you are never going to play WoW with another player with your toons and just use your own boxed toons, the choices becomes somewhat narrow until you are geared. This is especially true if you are limited in your desire to learn to control all the characters movement during fights and such.

I would keep in mind the ability to play the characters in different specs in LFG, since gear has an offspec stats now.

Transferring items from one character to another is just growing and growing in availability in the game. I really pays to have a character or two that can be played socially.

A lot more healer control will be needed from here on out, there are some healing spell changes that you need to familiarize yourself with.

There are changes to the on demand buffs for classes as well, so some of the burst on demand has changed. This is routing toward a proc system which isn't so friendly to most single button dps boxers.

This all said, content has never been more accessible to all players that now, if rewards continue to be frequently tooled up alternative or additional gearing paths are all over the place.