Honestly, I'm sure there are plenty of ways you could make that origin work WITHOUT diminishing Twilight's ascension (perhaps rather than a one-time thing, make it something that's so difficult that only Cadance and Twilight have ever been able to pull it off, and most other alicorns, including Celestia and Luna, are born naturally), but even with the faith I have in the writers of the show, I don't see them managing to pull something like that off.



Not to mention, if Skyla ever shows up in the series as Shining and Cadance's foal, she'll likely be born an alicorn, throwing a further wrench into the whole thing.