Alicornutopia

I'm not sure the setting itself would work, but have you guys considered using Fullmetal Alchemist-style alchemy as a magic system?

I am pretty enthusiastic about FMA and its alchemy, but I probably can't be arsed to rewatch the original series or finish watching Brotherhood in order to use the setting in any detail. Just lifting the alchemy does sound more doable. XD

What would it take to arse you to finish Brotherhood? The ending is wonderful. And painful. But mostly wonderful. You could also read the tail end of the manga, if that's more convenient.
Either way, that sounds like a fun Effulgence setting.

I stopped watching after like ten episodes, not because I didn't like it (I loved it), but because I just couldn't keep it up. I anticipate that rewatching/finishing would be a large time investment and this thought fills me with dread.

I watched all the way through an FMA, I think the not-Brotherhood version, and I'm not sure if Brotherhood is different enough to get around my usual aversion to re-watching things.

To my recollection (and I haven't personally seen enough of it to have gotten any more than a very rudimentary sense of this), they are pretty damn different - the cast of characters has high overlap, and many parts of the basic premise are the same, but it's like - the difference between Sunshine and original BTVS canon if Giles was the main character in both. A lot of peripheral worldbuilding elements and plotlines are totally changed.

The way I heard it was this: FMA the anime started running before the manga was finished. When it caught up with the manga, it diverged and went into its own continuity. Much later, after the manga was finished, they remade the show following the manga all the way through, and called it Brotherhood. I was told that of the two I should just watch Brotherhood, because the ending is infinitely more awesome. There are other slight differences I think, but that's the gist of it.

Upshot, you could get around your aversion to re-watching things by starting to watch Brotherhood around the divergence point,

Watching Brotherhood does not feel like rewatching FMA - it starts out feeling like a very fast recap, with some small differences that grow into larger ones, and eventually it takes on a life of its own, becoming a whole different show. The ending of Brotherhood is MUCH MUCH better. (Original FMA was ruined by the ending, IMO.) I found that Brotherhood dragged a bit in the middle and there were a few characters added who I wasn't terribly fond of (and a few added whom I love), but overall I strongly prefer it to the original FMA. However, Brotherhood blows through several major plot points that FMA spent more time on, which reduces the emotional impact of some events which were major wham episodes in FMA. Hughes dies in ep25 in FMA, but in ep10 of Brotherhood - 10 more episodes down the line and Brotherhood's plot has taken a major left turn from FMA's, and they end up going in very different directions. Oraanu is correct that you could theoretically just start at the divergence point, although I hesitate to say which episode that is precisely. I think the ideal watching experience would actually be a mixed cut of the two, if that were possible. Since that's not easily done, watching FMA and then Brotherhood is probably the best option.

I watched only Brotherhood, and the spoilered piece had *plenty* of emotional impact.

And yeah, they go very different directions, to my understanding. None of the alternate universes thing, homunculi are still related to the Philosopher's Stone but have almost no other similarities, the big bad is a totally different person (tied to the homunculi in a different way), and there are additional, more interesting underlying principles of alchemy, including a different but related system from Xing, the China analog.

Particularly interesting, there's a connection made between trying to bring back the dead, losing limbs, and gaining the ability to do alchemy without a circle, which I think a Joker might find really interesting. So even if you're not going to watch it, I'd look into that.

There is a connection like that in not-Brotherhood too. People who've watched both: How similar is the connection?