There are many who would contend that the most surprising part of this week's B&R announcement was the banning of Birthing Pod in Modern. Personally, I found it more odd that Dig Through Time was considered too good for Modern using a guilty by association argument with Treasure Cruise while not being part of the discussion of Legacy's Treasure Cruise ban.
Treasure Cruise was cited as increasing the power of Delver, Burn and, Jeskai Ascendancy Combo to the point where they pushed other decks out of the format. Their decision to also ban Dig Through Time was made because, "—while a Delver deck might use Treasure Cruise over Dig Through Time, banning one but not the other would do little to change the deck."
Meanwhile, Treasure Cruise was also banned in Legacy due to hyper-powering Delver decks and decreasing format diversity, however no mention was made about whether Dig Through Time could have similar effects on the eternal format.
I imagine that this decision was largely rooted in the fact that the difference between one mana and two mana is dramatically more pronounced in Legacy than in Modern. That said, Dig Through Time provides card selection much stronger than other options available at two mana.
Dig Through Time might not be great in Legacy Delver, but isn't it possible that another strategy such as Sneak and Show or Stoneblade could exploit it to the point of warping the format? Perhaps something akin to the deck Korey Mcduffie Top 32'd Grand Prix New Jersey with:
Time will tell whether Dig Through Time is safe for Legacy. For now, I'm left wondering why take the chance in Legacy that they weren't willing to take with Modern?
Think Dig Through Time is too good for Legacy? Think it would have been fine in Modern? Chime in in the comments!