The idea behind virtual sub-classes is a choice of a 99% cosmetic change to your character without adding new classes, specs, or mechanics. This would satisfy a good amount of desire for new classes without mixing up balance.
The difficulty would be giving each class a good sub-class, since some have some rather good avenues. Some would apply to the entire class, while others would modify each spec more independently. The aim is to make a class feel different, not play different.
The magic damage school would change on many specs, which is where the 1% of mechanical change comes from due to the 1% magic damage resistances, but I find them to be acceptable.
Ability names may change, or look quite different, but mechanically it is identical.
Death Knight - Runemaster
- Rune names changed.
- Frost becomes Nether (Arcane), Unholy becomes Felcraft (Shadow), Blood becomes Ley Infusion (Physical)
- Undead minions replaced by Revenants (seen in Northrend).
Druid - Savage Druid
- Bear form becomes Clefthoof, or other tanky animal that I currently can't think of.
- Cat form becomes Scorpion.
- Restoration becomes a Flame Druid, healing with fire.
- Unknown replacement for Moonkin.
Hunter - Mix
- Some change to pets used.
- Survival becomes Dark Ranger (Shadow and Arcane)
Mage - Mix
- Fire becomes Acid (nature), Frost becomes Hydromancy, Arcane becomes Chaos (green Shadow).
Monk - Unknown
- Possible visible weapon usage for hand attacks.
Paladin - Unknown
- Too much of a shadow theme, and shadow knight exists already.
Priest - Nemesis
- Holy becomes Desecration (shadow heals), Discipline becomes Entropy (shadow heals), Shadow becomes Lambent (holy dps).
- Shadow heals by reversing the process of getting wounded.
Rogue - Demon Hunter (Yeah I know, but Rogues were difficult and it could kind of work)
- Whatever a Demon Hunter would be, except poisons are now the demon magic.
Shaman - Mix
- Elemental becomes Poison (nature), Enhancement becomes Geomancy (earth and fire/magma), unknown for Restoration.
Warlock - Mix/Alternate Energy
- Demonology becomes Necromancy (shadow/arcane), Destruction becomes Sha (Fire), Affliction becomes something related to Old Gods/Umbral (shadow).
- Pets changed depending on spec. Necromancy gains undead Vrykul pet to replace Felguard, Destruction summons Sha, Umbral uses Old God minions.
- Warrior - Unknown.