Alright, here's a real question here:
It's like 2025 and Smash 6 is finally revealed. Echoes are a thing, and so is Chrom, but Roy is out and for some psychic reason we know he's out of base for good. Is Chrom still considered an Echo? If Roy came back through DLC, would he be an Echo of his own Echo?
Well, if you want a serious answer, I'd say it depends on whether or not he's been changed.
If he's been diversified from Roy, then he'd no longer be Roy's echo, and could probably gain a designation of his own. However, if he's still the same, he'd probably still be considered a Roy Echo.
Remember that all Smash characters are now designated with a number, and that Echoes don't have a unique number. So if Chrom were to be readded, he'd probably still be internally classified as 25E. Whether or not that's still be the standard system for characters at that point, I don't know, but it's probably good to keep in mind.
Were Roy to be readded to the game later, he'd probably still be fighter #25, and Chrom would still be his Echo.
Chrom/Roy isn't the same as, say, Simon/Richter. They weren't introduced at the same time, Roy as a whole came first. Both his inclusion
and his remade moveset were set in stone long before Chrom as a playable character ever graced Smash, so it wouldn't make sense to make Roy an Echo of Chrom, since Chrom is the one who takes from Roy.