First Officer reported crossing hold short line then seeing an aircraft on opposite end of runway on take off roll. The other aircraft took off first.

Narrative

Upon receiving our IFR release in Gunnison from Denver Center; we made our radio call on GUC CTAF with our takeoff intentions and crossed the hold short line for Runway 24. Before turning onto the runway (but passed the hold short line) we noticed Aircraft Y in position on the opposite runway for takeoff; VFR. I made another radio call; calling them in sight" and that we were stopping where we were. We heard no response; and Aircraft Y proceeded to continue with its takeoff despite the fact that we were effectively on the runway; being passed the hold short line and perpendicular to the runway. Aircraft Y climbed out with no incident and no radio calls. Once clear of traffic; we continued with our takeoff. Once reaching 9300ftMSL; we contacted Denver Center. Shortly after; Aircraft Y checked on as well. The Captain (Pilot Monitoring) asked Aircraft Y if they were on Gunnison CTAF. They responded saying they were.The situation could have ended worse; had we not noticed the aircraft on the opposite runway (RWY06). We could have done better by visually clearing the runway before crossing the hold short line; however the cresting runway made visibility hard to begin with. There is also the possibility that we did not hear their radio call announcing their intentions to takeoff from Runway 06; however the Captain and myself do not recall hearing any radio calls from them. Aircraft Y's communication was lacking and their decision to continue with their takeoff was unsafe. No further incident occurred.Cause: Lack of communication from the other aircraft. Several other aircraft were arriving and departing GUC and we heard all of them except for Aircraft Y.Suggestions: Better communication from the other aircraft. They also could have picked up their IFR clearance on the ground like everyone else; that way they could have heard everyone else and not departed until receiving their release."