>Is there actually an essentials version of literally everything,
Almost everything, yeah. Assassin, rogue, barbarian, fighter, sorcerer, wizard, cleric, paladin, fighter again, warlock, two different flavors of ranger, wizard again, wizard again, druid, blackguard, vampire (avoid this, literally the only bad 4e class)...
The only things that come to mind that DON'T have an essentials variants are the warden, the phb3 classes, and the warlord, because warlord doesn't really work without the encounter/daily/at-will split.
>Can you incorporate/allow daily powers on an essentials character
Depends on the class. Most of the 'casters' (cleric and wizard) keep daily spells/prayers and seperate encounter spells but that's why I said ban them earlier. I THINK Sha'ir wizard doesn't use dailies but if it does just use Elementalist sorcerer. No dailies there.
>such that you could make use of all the existing powers in a character with a unified resource pool?
Almost every Essentials class (see above) has a single encounter power that they can use multiple times. Slayer fighter, for example, just has a bunch of at-will stances and a single encounter ability. Where other 4e classes gain powers as they level until they reach a maximum of 4 encounter powers (after getting a paragon path), the essentials Slayer gets 4 uses of his single encounter power.
Psionics, on the other hand, buffs their at-will powers using Power Points, and tend to have certain effects happen when they're out of power points. The exception is the monk, which works differently to psionic and regular classes.
>most of the discussion I've been talking about shadowrun style strain rather than an mp system, i only tangented into mp because thats what everyone else kept bringing up.
Strain works for shadowrun but not for most other places and certainly not for 4e. An mp (actually two mp) style resource system already exists in 4e without removing everyone else's 'classic' option.