While I agree simplicity is a good result to strive for, I don't think that arbitrarily making some tech-based and others psi-based (or just Jace) can be considered "simple". Besides maybe Gideon, what other Planeswalkers' (lol Skywalkers) magic has no possible psionic equivalent?

Ajani, Domri (hate him) Elspeth, Garruk, Karn, Kiora, Liliana, Nissa, Tezzeret, and Tibalt.
We don't know enough about Tamiyo so...
An argument could be made for "mental psionic bonding" in the case of Domri, Kiora, and Garruk but... to be frank, that seems an extra layer they just don't need, except in the case of Kiora, who has the whole aquaman angle to take. It serves the character better for Garruk to just have well trained trophies, play up the Predator angle. I don't care enough about Domri, so whatever.

Of the possible uses of natural, mentally based psionic abilities, we have Ashiok, Bolas, Chandra, Dack, Jace, Koth, Ral, and Xenagos.
However, there in, Ral and Chandra both feel more appropriate as tech based characters because there isn't any real reason for them to HAVE kinesis.

Notable absences from both above lists are Sarkhan and Vraska, who I think benefit best by Sarkhan being capable of metamorphosis and Vraska just having alien biology.

Well, I do generally disagree with a decent few of those, presume any who can should use tech,

1. How would you assume 'teleporting' to work for the MtG cast? (and just to clarify, I am meaning StC's equivalent of summoning

2. How would Ajani go about using Crystal (and/or Pyre & Xeno) Psi to produce Augments and Graft them to allies?

3. How would Jace use Cryo Psi to actually use mental powers in a way that does not overlap with 2?

Open rift, troops step through.
Ajani has exactly one iteration which cares about Auras. It is, in actuality, an aberration of design. There are only, really, 3 really solid, unbiased designs that you can apply to Ajani. Ajani Vengeant, Ajani Goldmane, and Ajani Steadfast. Ajani, Mentor of Heroes was ultimately too biased by the environment it was released in. It came in a block that heavily shaped its development. Caller of Pride just... does things that Ajani doesn't. They really wanted Elspeth's abilities in the year they designed him, but didn't want to use her character apparently.
Jace's mental abilities don't require mana to start with. They are inborn.

The same rift that makes them StC 'walkers? It's implied not only Planeswalkers can summon. I'm not talking about his Planeswalker cards, I'm talking about him as a character. As an opponent in multiple Duels he relies on aura cards, and most of his "soul's _____" spells are based on Auras. Auras and avatars seem to be his specialty. All the same, I was just using Ajani as an example. Where is it said Jace's mental abilities require no mana at all? I would figure Jace would inject himself with Cryo Psi to facilitate his own psionics, but then that may or may not overlap with the methods of administering augments/grafts.

That's why they specified that tech was involved in the format of this. However, as I said at the start of it all, that discounts the unique aspect of the characters who are nominally our protagonists.
His soul's _____ cards don't use auras... They deal with power.
And I'm still afraid that auras just... aren't his specialty even if he uses them in Duels, which is a sketchy source to take into consideration to start with, even if they've tightened themes up a lot since the first go around. Soul Magic, healing, these are the things that he's best at, and just as easily, things that could be accomplished with TECH.
In no lore, anywhere in his appearances, has he used enchantments.
Agents of Artifice. You know, the thing that set the entire foundation for his character.
His mental abilities are inherent, not something he has to cast.

It was said that teleportation alters the object being teleported, but the 'warlords' are unaffected by space travel. I'm fairly certain that the "Soul Magic" you're talking about is more often than not the lore-counterpart to enchantments. The "can't use soul magic on himself" thing further suggests this. Oh. Is he the only character at all with inborn magical abilities like that? All the same, how would augments and grafts work aesthetically you think? Liliana's abilities may change in some pretty creative ways... lol Chain Veil = visor.

Yeah, but I'm not sure how that actually applies, because what we saw them display didn't... really seem that different.
The only thing I can think of is something like completely blank slates that adopt traits depending on which alignment they are summoned to.
but it's not. We know exactly what his soul magic is.
Soul's Might, Soul's Fire, Soul's Majesty, Soul's Grace. This is clearly what his soul magic is. I mean... it's explicit in every possible way.

Well, Bolas has his mind destroying touch. Everyone else is pretty baseline human except Ajani's ability to see someone's soul.

I actually see the Veil as being as much a digital artifact as a physical one and what was done to her as much a case of subdermal cybernetic enhancement as well as nanite modification. Not enough for her to be considered a cyborg in any significant way, but enough that she's not baseline human anymore. Anyways, the veil would, theoretically, remove the safeties on the tech that the demons had used to enhance her.

As for augments and grafts, I view them as long term gene treatments or cybernetics.