Yeah, that’s a reasonable concern.

I’ve written a couple of things that parse text decklists (you can find them here). For what they do, usually it’s safe to just ignore any line that doesn’t start with a number. That’ll be okay for decks in this new format… unless the deck name starts with a number, which probably isn’t that unusual. I actually have a [[Slime Against Humanity]] deck on Arena right now that I named “24 Slime” (because that’s how many copies it has).

The simplicity is the point of the text format. It would have been better for them to make a new format to support this new feature (while still supporting the old text format). MTGO had .dec and .dek formats that could perhaps have been reused for this. Then again, part of the appeal of the text format for Arena is that you can just copy it into your clipboard, instead of having to save a file somewhere. I don’t remember whether .dec and .dek are binary formats. But let’s say they are – there are still plenty of text data storage standards, like JSON or YAML, that Wizards could have used to create a more complex, but still copiable, decklist format.

Edit: Actually I looked at the new rules again and I’m wrong, “Name” will always be the first thing on the name line, and that shouldn’t bother either of my programs. But I still feel like an entirely new format might be the right idea. The fact that they created a whole new “About” section means they think they might add more fields to it in the future. Who knows how complex those fields might get? Switching to an established standard now could save them some pain down the line.