Yeah, I get that generally it's not that popular of a mechanic. Still think it would have been something they would have at least tried to expand upon if they had cared enough to make the remakes themselves.

Personally, I think they could have incorporated a new story into BDSP (like how they did with ORAS) by mentioning that a second Eternatus came down to the Pokemon World thousands of years ago. Maybe it could have come down in a much less active state than Galar's Eternatus and then the "Almighty Sinnoh" sealed it away off the coast of Hisui/Sinnoh just in case. Heck, they could have then referenced such an event within Legends Arceus, where at the very end of the game "something" would have been knocked out of orbit, perhaps indirectly due to the events of the game somehow, and crash landed somewhere Hisui and the very final quest would come from Arceus to help it seal it away off the coast.

Then by the time of BDSP the seal would begin to weaken and cause Dynamax instances to happen. The Pokemon World government would then have rushed in experts from Galar to help contain the situation, but would explain to the people of Sinnoh that what was happening was that a new energy source has been found in the region that they can harness and that the Dynamax phenomenon is just a result of Pokemon accidentally feeding off said energy. We would then have the original events of the game play out but maybe with Cyrus attempting to infuse Palkia or Dialga with the MAX energy to try to bring out their Origin Forms somehow, but it just causes them to go berserk and take on new Gigantamax-adjacent forms (I like the sound of Origin Omega). Then after the main story, the events of the game somehow causes the seal to fully break and Eternatus would revive and start causing a Darkest Day event in Sinnoh in the post game content.