The existence of Forgotten Empires was the reason I didn't choose to purchase the HD version when it came out. Simply, FE was superior in every way to what was on offer. It's really great to see that the official developers have recognised that these guys did an absolutely incredible job, a real labour of love, and want to integrate it into Steam. Means I may have to get that HD version after all.
As an aside, I would be disappointed if this has to be purchased. The original developers have released this for free for many years because they were passionate about the game and improving players' experience. If this were to be cashed in, then it would sour the entire effort.