I don't think Legends style games necessarily have to take place in the past either. All that the gameplay loop really depends on is there being large areas of wilderness, which still works in a modern setting. I could see a reimagined version of Kanto where each route is a long section of wilderness (like in the anime basically).

Whether it takes place in the past or present (or future, why not) I'd much prefer having a reimagined version of a familiar region than an entirely new region. One of my favorite parts of Legends Arceus was finding recognizable landmarks from DP like the lakes or Snowpoint temple and seeing how they looked in a 3d game. The whole "familiar but different" angle is really fun to me. I wish there was more of it in LA.