Reverse 1999 just revealed its first "alter" in the newest story trailer for CN server. In gacha parlance, an "alter" (presumably short for "alternate") is a version of an existing character. Arknights has lots of these.

It makes sense, Eagle was much younger and inexperienced when she first showed up in the default roster as a 4-star (as shown in this old poster). This is one way to show young characters growing older and honing their skills, certainly cleaner than using Skins.

FGO is no stranger to alters via swimsuit variants (and the literal Alters). Limbus Company has only 12 playable characters, so the gacha ONLY has alters for them.

But why did I still feel heavy? Perhaps the possibility never crossed my mind, that it seemed like it wasn't a thing Bluepoch considered.

Considering what the 3.7 story chapter trailer depicts (an attack on the SPDM), this really is an end of an era (or at least the status quo).