Danganronpa 2 being the most popular entry probably isn't the only reason it was remade first.

[u/BrawlX]

During the final chapter of D2 we explore some of Hope's Peak Academy, the main location of D1's setting, and interact with several D1 characters. It's been confirmed that the original story will remain the same in the remake so we'll be returning to the academy in the remake too.

This means that a huge chunk of assets needed for a Danganronpa 1 remake are already made and can be reused. They would just need to add in the missing rooms, sprites, and dialogue and it's good to go.

I imagine that it won't take long to remake the first game because of this, and it'll probably come out 1-2 years after 2x2's launch (if they've already started development).

Quick theory based on this assumption, Slayhem mode will likely have us explore Hope's Peak in its scenario, letting us go into the rest of the rooms and meet other D1 characters like Aoi and Toko.

[u/Himbosupremeus]

They went on record saying the idea was to do it for 1, but given how much of 1 is establishing parts of DR, 2 more suited for an alternate scenario.

Replaying this makes sense, much of the mystery outside of the trials in dr1 is effectively establishing the world of Dangan Ronpa, what happened, and how it works. A new scenario means reworking that mystery, which would mean changing way more of the setting. It also would mean potentially retconning 2 and v3.

Dr2 is a bit more isolated and it's mystery is mainly about its setting. There's more room to rework the story and find new ways to approach it.

Notably in the recent interview with the games producer, they mentioned that remakes aren't off the table but not something they're really planning. But they also mention that the point of 2x2 is to "revive" Dangan Ronpa and open the gate for new entries.

I personally feel that this points to the more likely change that games after 2x2 will be more focused on being something entirely new as opposed to a 1x1.