DM: Although, now that I'm thinking about it...
Twilight Sparkle: Is there a problem with my plan?
DM: I mean, it makes sense for Twilight to look into that, but it might be more difficult to actually accomplish than she might hope. The concept of all magic existing in a unified field is still largely an unproven theory. The only creature who could reliably detect meaningful ripples in magic-type is... ironically enough, Discord himself. I mean, I don't want to leave you with NOTHING to do... and you've certainly pulled off incredible magical feats already... I'm just not sure what you can realistically do before Discord makes his next move...
Rainbow Dash: I think we're fine without homework.
Rarity: We all knew this was going to be a strange session.
Pinkie Pie: And I know strange!
Twilight Sparkle: If the ball's in Discord's court, then we'll wait and be ready. Don't worry about us.
DM: ...Thanks.
Applejack: ^Well, keep worryin' about us a /little./^
Part of the eternal problem of adapting a TV show to a D&D campaign is giving everyone something to do when the medium focuses on one series of events and a limited number of characters at a time. And it gets even weirder to keep all the plates spinning while mixing multiple episodes together! Buuuuuut I've gone on and on about all that before, I'm sure.
Actually, this could work better than if there was just a book with "how to detect chaos magic" in canterlot- the DM can make it a quest to research what they would need to track down discord/ where they think he might have gone to, and plan little one offs for their various attempts- Ironically the long running sort of thing he intended Nightmare Moon to be, instead of it being fixed in one session.
For the comic, that means various odd episodes can be used to explore the various things they are doing and places they are going searching for clues, and doing research.