A planet very much like "Proxima b" is already in the game.
Eden: 0.66 Earth-masses, orbital period 31 days.
Proxima b: ~1.3 Earth-masses, orbital period 11 days.
Frankly, given that Eden is an entirely fictitious planet and the scientists back in the 1990s (when the Alpha Centauri system as it appears in ED was first designed) were saying that Proxima probably didn't have any planets, the statistics for Eden are close enough to the truth for Braben & Co. to be considered a prophet. The only thing he got wrong was the discovery date (Eden was not discovered until 2038). Granted, Eden is smaller than Proxima b, so would have been harder to detect if it had been there instead.
According to ED lore, Eden was the first planet outside the solar system where water was detected; it helped spur on the first interstellar probes, hoping to find Eden a paradise planet ripe for colonization. The fact that Eden was an aqueous-greenhouse hellhole proved something of a disappointment, but the scientists stayed and built an inhabited outpost there anyway. Hutton Orbital is the end result.
IMO, they shouldn't add "Proxima b" to the Centauri system. If anything, they should simply tweak Eden's stats to make it slightly bigger and slightly closer to Proxima.