So I'm gonna pick apart at what the OP's suggestions were and try to bend them in a way that I think would work more for XIV since some jobs in the series don't exactly translate as well (amirite Blue Mage fans).
So when I think of a job like this, I sorta see them as the ultimate abjurers (shielding spellcasters) moreso than Scholar. It could also work off a mechanic like a Verse gauge, where one spell grants one Verse and a number of Verses can be used for various stronger spells. It's like Orator from FFT if it made slightly more sense for this game.
Also a bit on the fence about scrolls as weapons, but that's just me. Maybe a massive tome or libram as a weapon and the cast animation being the character holding their hand out as the pages fly across.
So this one has always traditionally been a big fat "no" just because percentage-based heals used to be a thing with Scholar via Lustrate as a "25% of max HP" heal, and was later changed to a flat potency total in Heavensward because it was just too much of a pain to balance and wound up either being far too powerful in circumstances where healing may be limited in some way or far too weak in circumstances where heavier healing was required.
As cool as it is, it's sadly just one of those ideas that just doesn't work outside of FFT without extreme mutilation or getting the Blue Mage treatment.
Setting aside the fact that the word for "Summoner" and "Evoker" in Japanese are nearly the same (both versions translate to "summoner"), this is another idea that just wouldn't work at face value without either getting the Blue Mage treatment or something to more adequately distinguish it from Summoner (translation: it can't use pets unless it's vastly different from how Summoners can use them).
That being said though, Evoker I'd argue is about as close as we'd ever get to a "non-limited Blue Mage", as the "evocation" bit could be bringing out monsters not as pets, but rather as personas with various attacks changing depending on which monster you have "evoked". Unfortunately though, any real attempt to make it multi-role would wind up in the job being limited because of how players would use (or more likely abuse) the system.
The "drain" theme could actually go into a different job entirely, and I could see something like that working like the Archon soul from Rift, where you provide group buffs at the expense of your stats while applying stat drain effects to enemies to regain the stats lost from your group buffs.
As you say though, Lanista as a job really just is a glorified Dark Knight. We also already have role skills that provide stat debuffs, but they have to be kinda bleh in order for them to be balanced.
As much as I'd REALLY love to play this, I know it would only happen as a limited job and the dev claim would just be an image of a roegadyn on their chocobo standing in front of a mob with a confused character in the foreground of the image with the tagline "where's the mob?" alongside an argument that having such a giant character would be too obscuring in a regular fight. The only way I could see this working as a standard job is if the chocobo was a cooldown and it was turned into the chocobo equivalent of Dragoon in FFXI, which you'd likely agree that it just wouldn't be the job we know and adore.
I'm also going to say something that even sickens me, but it will make sense: Chocobo Knight would be better off as a limited job. I say that because by making it a limited job, it would instead provide a more personal story using your own chocobo, and because you already can't bring your chocobo companion into dungeons, it would allow for building off of mechanics already in place with the chocobo companion system and thus providing a more adequate solo gameplay experience.
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With all of that out of the way, I would love to see jobs that break stereotypes commonly associated with fantasy roles. Psychic is a great example of this as a caster DPS or a healer that isn't quite a traditional spellcaster. Grenadier as a healer, or something like Chemist using a more tech-themed means of providing heals as another example. How Dancer will be implemented is a step in the right direction, but I think this is probably the best way we could get a puppet-themed job (as in not FFXI's Puppetmaster). While I'm curious about Gunbreaker, unless the tank stat changes of Stormblood are reversed, the only tanks we can realistically get are the stereotypical heavy-armored tanks, meaning that we'll likely wind up with more heavy-armored jobs new to the series; that's not a bad thing.