Wizard/Sorcerer, Fighter/Ranger, Thief/Bard and such really mostly redundant to me. They seem like they are combos that are 80-90% the same mechanically. If anything, I'd like to see a Class, Theme, Kit, Background scheme rather than a proliferation of mostly redundant classes.
Thus, you could have a Fighter [Class] (Paladin) [Kit/Sublass] Slayer [Theme] Soldier [Background]. And a Fighter (Knight) Cavalier Noble. Or perhaps a Rogue (Bard) Blade Performer. Maybe a Rogue (Thief) Trapspringer Urchin. Or a Mage (Invoker) Bookbound Academic. Possibly a Mage (Warlock) StarPact Thrall. Or a Priest (War) Crusader Wanderer, whose much like a paladin. Or a more classic Priest (Good) Cleric Templeborn.
<EDIT> You could also get campaign specific priests like Priest (Helmite) Champion Mercenary. Or Priest (Druid) AnimalWhisperer Hermit.
Likewise, it might also solve the CS conundrum for the ranger, paladin, barbarian and other "fighter types" - they could explicitely be given CS dice but their kit could express how its used - favored enemy fo rangers, smite for paladins, rage for barbarians, panache for swashbucklers, showmanship for gladiators, ki for samuria, etc.
Likewise for mages, kit could define how you use your magic -Vancian for wizards, pacts for Warlocks, arcane blood for sorcerers, truename, shadow magic, wild magic, whatever system you want to attach to the kit/subclass portion. Same for spheres/gods/spirits/nature or whatnot for priests. Again, you could then attach various subsystems to rogues to have special abilities to make the likes of bards, assassins, charlatans, beguilers, etc.
You said it: MOSTLY REDUNDANT instead of FULLY REDUNDANT, the other 10-20% that doesn't overlap (and I think that the non-overlapping parts are at least a 30% or more) is what makes multiclassing worth -from a mechanical point of view, because there are more reasons to multiclass than simple optimmization/munchkinism- and what actually makes the classes unique. Rogue-bard is one of my favorite MC combos (along with fighter-bard) and I can tell you they really doesn't share as much as you'd think
What bard and a rogue have in common in 3.x and 4e:
- More trained skills/skill points than average, some overlap in class skills
- Medium BAB (3.x)
- Good Reflex save/defense
- Some weapon proficiencies
- Light armor proficiency /cloth and leather proficiency
And that is pretty much it.
What the bard has that the rogue lacks:
- Access to knowledge skills as class skills. (automatic arcana trainning on 4e)
- Good Will save/defense
- Proficiency with shields
- Better weapon proficiencies
- Better armor proficiencies (4e)
- Bardic music (3.x)
- Party support abilities (4e)
- Spellcasting (3.x) / Arcane powers (4e)
- Overall versatility (4e)
What the rogue has that the bard lacks
- All thieving skills as class skills/thievery as class skill
- More skill points/ more trained skills
- Hand crossbow proficiency (3.x)
- Single target damage potential (sneak attack)
- Trapfinding/trapsense (3.x)
- Battlefield Mobility abilities
I don't think those differences can be contained inside the rogue's scheme as we know it, as it only contains skills and a trait, and I cannot think of a way to make them fit into a 3-4 feat package and even there it isn't satisfactory, since you don't get full bardness until you reach a high enough level and you ares consuming an important customization resource to get a stereotipical run-of-the-mill bard.
And if you think Ranger/Fighter doesn't make any sense, I have a one word answer to it: Drizzit.