There are large questions about B that I have and they relate directly to:
1) The relatively weak "payload" of 5e feats as PC Build Resources with respect to the "payload" of 5e Class Features.
2) Whether or not 5e is going to include unique Paragon/Prestige Classes (the answer to this seems to be all over to the place).
There are a number of iterations of Fighter/Mages ("Gish" classes) that are quite distinct from one another (from both a mechanical standpoint and the accompanying fiction/archetypes that those mechanics represent). I'll outline the primary 4 that I can think off of of the top of my head:
1) Bladesinger (Primarily Duelist Fighter with secondary arcane support. This class is probably the most "Jedi" of the classes and is basically a re-skinned Martial/Arcane monk who uses a sword):
Proficiencies/Primary Attributes: Light armor, One-handed swords. Dexterity and Intelligence.
Combat Style:
Defense - Relies primarily on borderline supernatural speed and tactical mobility/spell-casting (abjurations and transmutations) and finesse/speed based swordplay.
Offense - Martial Blade-flurries (speed and precision) primarily. Has limited use marriage of spell-casting and swordplay to attack with both simultaneously.
2) Spellsword (Primarily Slayer Fighter with secondary arcane support. This class is very much the "Arcane Warrior" from Dragon Age. Very Fighter/Cleric-like in "feel."):
Proficiencies/Primary Attributes: Heavy armor, Heavy weapons. Strength and Intelligence.
Combat Style:
Defense - Relies primarily on Heavy Armor as archetype is the only Fighter/Mage able to cast spells while in Heavy Armor.
Offense - Able to Channel Spells directly through Melee Attacks.
3) Hexblade (Fighter/Warlock hybrid rather than F/M. Like the standard Warlock, this class makes bargains with extra-planar Powers - Abyssal, Infernal, Fey, Shadow - for their extreme, yet dangerous, might)
Proficiencies/Primary Attributes: Light/Medium armor, Light or Heavy weapons. Charisma and Constitution (or Dexterity).
Combat Style:
Defense - Contingent upon extra-planar Power bargained with, will leverage either Light Armor and Dex or Medium Armor. Access to powerful warlock spells/summons to augment defense.
Offense - Access to powerful warlock spells/summons to augment martial offense.
4) Swordmage (The only "hybrid" that is almost exclusively a Wizard. Martial is very secondary for this class. The most "Gish"-like of the classes given its heavy use of teleport effects. Basically a Wizard trained for infantry, front-line combat who channels spells through a sword):
Proficiencies/Primary Attributes: Light armor, One-handed swords. Intelligence and Constitution (or Strength).
Combat Style:
Defense - Light Armored warrior who relies primarily on powerful Warding spells and arcane spells (Teleports) to augment tactical mobility. Melee Defender with ranged action denial/control (or action denial/catch 22 by proxy of Marking/teleport system).
Offense - Almost exclusively through Arcane, control, AoE spells channeled through sword. Contingent upon Swordmage Discipline, may have secondary damage source through Marking/teleport system.
These builds/archetypes are all extremely different from one another mechanically and within the fiction. Given the lack of "potency of payload" inherent to feats/specialties (at least in this iteration) and nothing resembling their distinct mechanics within current class build structure, I am QUITE unconvinced that standard, generic multi-classing and feats/specialties will produce the distinct mechanics and resultant fiction of these builds/archetypes at this point. If that is so then they either must be classes of their own or there must be a strong Paragon/Prestige Class system. So if they have no Paragon/Prestige Class rules then I lean toward your option B. However, there must be multiple classes. My preference would be a much better payload for Feats/Specialties and a strong Multi-Class system.
