We shall call them "scrolls" for lack of a better term for now. As Barbarians are generally dissuaded from learning Arcana, the ability to read and study them will be based on a check with another skill (I suggest either Perception, Appraisal, or Tactics).

Magic users will be unable to study or use these scrolls in any way, like NMUs cannot use magic scrolls. Something unknown about undergoing the process of attunement reconfigures something about the humanoid anatomy, whether in the brain or elsewhere, that shuts off an MU's access to these abilities. Activation uses the same verbs as spell scrolls.

Barbarian abilities available via scrolls:

Buffalo	Monkey	Famine	Screech	Swan	Bear
Anger	Focus	Embrace	Unyielding	Python	Seek
Rage	Tornado	Landslide	Pirahna	Owl	Staunch

Reasoning: Thieves will be able to emulate the basics of martial prowess (forms), presence projection (i.e. roars), mental focus (meditations), and emotional manipulation (berserks) to achieve many basic or even advanced Barbarian forms. They will never be adept enough to use masteries. They lack the focus of magical wards that the Barbarian guild has, so more potent magical barriers are out of their reach. Anything esoteric involving direct manipulation of inner fire (i.e. using Volcano to avoid death at the cost of IF) is forever out of reach.

Thief abilities available via scrolls:

Avoidance	Elusion	Flight	Safe
Plunder	Focus	Sight	Steady
Darken	Dampen	Speed	Spar

Reasoning: Barbarians can emulate the Thief style of combat with weapons (outside Backstab), as they are not total strangers to use of stealth, guile, or more "dishonorable" methods of combat. They are also quite capable of wrapping their brains about survival skills. However, they lack a Thief's innate understanding of movement and concealment. Anything regarding invisibility is off the table. Any Special-category khri are out of reach, likewise with Tier 4 khri.

>Just glancing at this list there's an absurd amount of overlap for a bandaid that would only be available to the two guilds.

1) Any number of spells available via scroll are generally undesirable (i.e. 7 of the 8 magic guilds have no use for Teleological spell scrolls, and even many Moon Mages aren't interested in spending slots to perma-learn them). The intention is to establish a clear proposal for an NMU equivalent to Sorcery, not ensure literally every named ability is a top-tier PvP option.

2) "Needs of the many v. needs of the few" is a factor in determining development, but not the only factor, i.e. Paladins just got a SMITE rewrite because they needed it. Thieves are getting more khri because they need them. I'm not suggesting the GMs drop everything to do this, but NMUs would heavily benefit from some equivalent to Sorcery, so "only two guilds" is an irrelevant objection IMO.

>While this represents a "better than nothing" solution, I'm also dead certain it would be more complex to implement than simply putting Thieves and Barbarians into the magic system proper at which point my lore justification for them being able to use scrolls is that they figure out how to duplicate or mimic the spells as makes sense.

I never suggested this would be quick! For example, how do Thieves "use" inner fire on a technical level? But literally any game development requires work, so that's a non-factor. Do you feel the approach is erroneous and have a better idea for implementing some NMU equivalent to the Sorcery system? Now, that's much more constructive discussion, please feel free to provide such.

>About the only thing Thieves would really want from Barbarians is the Stamina buff and Wards. I think the only thing Barbarians would genuinely want is Dampen, Haste, Plunder, and maybe Steady. (Although that assumes Owl ever gets darkvision added. Otherwise Sight would be kind of attractive.)
>Meanwhile I think Thieves' want list is basically Cyclone, Tornado, Swan, Bear, and Screech.

100%. As both a Thief and Barb player, you have the exact same list I do for "desirable" abilities, but I refer back to point #1 about this being intendd to provoke big-picture discussion about NMU sorcery.