Queen's Gambit was just what an addon should be...a new island, a couple of new campaigns, and that's about it. A large portion of the Arma community never got it and it didn't hurt them.
I also think you've got a mistaken view of the time line, since I think Resistance came out less than 2 yrs after OFP did but offered major enhancements to the engine. Arma 2 came out almost 3 yrs after Arma, but Op Arrowhead is coming out less than a year after Arma 2. I think it basically is going to be Arma 2 to the current patch level with new units, terrain, and campaigns/missions. That's why it will integrate with Arma 2 or simply stand by itself. Of course, Arma came out 5 years after OFP, so by comparison Arma 2 was a quick release.
As for PC requirements, what it needs isn't all that much by today's standards. I know it runs fine on a friend's 3 Ghz C2D w/9800GTX+ on a 1920x1200 monitor using FSAA, and that's an over 2 yr-old configuration that wasn't even that pricey when it was new. Again, OFP ran miserably on most people's PCs when it was released, and it wasn't until the release of Resistance that the mainstream hardware had caught up to the engine.