When it comes to the question of hybrid or new classes, I usually like my "class morph" idea better then any other I have seen so far. So, I shall just repost it once again here, current revision:

Personally I would think the best way to add more "classes" is to give each class, say, three different "class morphs", each with its own new skill/passives line. Perhaps becoming available after completing cadwells silver/gold... to reward people who do play through that - a variation of the idea was to let them do the class morph after silver, and let them pick a cross-class skill line (basic class skills only) after gold...

Some possibilities:

Dragonknight
- Berserker/Gladiator (offensive self buffs & warcries; effect color: red/orange)
- Pyromancer (flame resist and even more fire; effect color: yellow/blue - gas flame!)
- Warlord (defensive group buffs, AoE standards, effect color: purple/gold)

Nightblade
- Illusionist (illusion summoning, mind magic; effect color: red/black - NPC illusionist)
- Monk (melee support & assorted “matrial arts style” magic; effect color: blue/purple)
- Ranger (animal summoning and nature magic; effect color: brown/green)

Sorceror
- Cryomancer (ice magic, effect color: white/clear - NPC cryomancer)
- Necromancer (death magic and undead summoning; effect color: cyan - NPC coldfire)
- Spellsword (melee support & buff magic; effect color: yellow/orange)

Templar
- Druid/Shaman (nature magic, totems, animal summons; effect color: green/brown)
- Paladin/Crusader (melee support and aura-style buff magic; effect color: white/gold)
- Witch-hunter (counterspells, spell resistance/shields, silencing; effect color: purple/red)

Another possible idea was to not only have an added skill line with its own flavor of visual effects, but maybe even morph the existing effects to match.
So for example if a sorceror goes necromancer, their spells might be color-shifted to necromancer “coldfire” cyan, summons would be morphed from the daedric familiar/clannfear/twilight/storm atronarch set to necromancer stuff like skeleton, flesh atronarch, wraith, bone colossus... and if they turn cryomancer, their dark magic crystals will turn ice-ish in effects, spells will get color-shifted to white-blue or white-purple, and their summons will be something along the lines of wisps, ice wraiths and frost atronatrchs... or a nightblade going ranger would have their reddish effects recolored to something nature-ish green & brown... that sort of stuff. For more visual goodieness and varietee between classes.

...of course, all those quick ideas are just very rough concepts, without much consideration but character fluff. I merely tried to give some options, and went for three instead of just two "magica-specialization / stamina specialization" - It's supposed to be more for added character diversity then anything else after all.

Thus for example with nightblades, there might be one magica-caster based with "illusionist", one stamina melee based with "monk" (Yes, a nod at the old D&D class of the name, the first "martial arts powered" class I remember in fantasy gaming) and one pet based as "ranger" since nightblades mesh very well with bow, and giving them woodland creatures for the "hunter" playstyle would seem applicable.

Similar thoughts for the sorceror - spellsword for stamina sorcerors, cryomancer since ice staves have no matching skill line yet (while fire and lightning staves sort of have), and necromancer because all too many people really, really want that...

Templar... the druid/shaman is a very natural idea, between breton wyressess, argonian treeminders and bosmer spinners, nature magic meshes very well with Templar healing and sunlight-powered spells; paladin is for stamina templars and a nod at the old D&D class of the same name (possibly subject to TES-ification change), and my "witch-hunter" idea is kinda inspired by the spanish inquisition (Yes, I know noone expected that ), its "warhammer" imperial counterpart and also "Dragon Age", I admit it... seems logical to set up the aedric-flavored templars as natural enemies of the more deadric-flavored sorcerors...

Dragonknight I had the fewest ideas, since I kinda dislike that class. More fire magic for dragonknight magica-casters with pyromancer is a natural first thought... so then I went with "leader-style group play support" and "berserker-style single combatant" flavors, though there may be better ideas then those...

In any case, since more diversity is always something I would love to see... much more fun having more choices in realizing your “perfect” character, especially since the limited number of skills one can actually use at any one time (5+U) makes people having to think and choose anyhow, so adding more active skills only increases a characters choices, not exactly their power...

And yes, spellcrafting might be able to cover some of those... but spellcrafting won't give you passives, which these skill lines should.

And while they currently have no intention of implementing aynthing class-wise, I really do hope they will do something like this someday. Since a fourth class skill would really be interesting, and having the ability to pick one out of a few choices... might add tons of character diversification, which for me is a very good thing...