Here's the link to that article where this rumored news originated. While I definitely think that it's plausible that that's what they're doing, it's still not confirmed quite yet. If that is where they go with it, I'd have to say that
@The Mad King is probably spot on, as they'd be re-adapting some Legends canon that's been seeded in bits and pieces since back in
Clone Wars, (scrapped scenes with Revan on Mortis & mentions of Darth Bane in the Lost Episodes)
Rebels (the ruins on Malachor), and the comics for
Lando &
Fortress Vader (Momin) as well as the
Vader Immortal game (proto saber).
If they wanted to tie into it, there's always the stuff that they could start with using the Dark Saber (since that has an easy ability to draw connecting context to
Clone Wars,
Rebels, and potentially
The Mandalorian), and use that to look at other ancient lightsabers like the one that Ezra found in Rebels on Malachor. There are a lot of good venues for large-scale conflict that would be interesting to see in an era before Anakin and The Balance and all the Skywalker Saga came into place.
All-in-all, it's a good direction to take if the rumors turn out to be accurate.
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