MGS3 is more like a spin-off / filler for MGS series.

The true series is from MGS1, MGS2 & MGS4. After all, the games focuses on Solid Snake.
But yeah, MGS3 is THE BEST of them all, even though it's a filler. Wondering if Kojima would do spin off for The Boss. I mean, what happened to her life before, during the space race, the World war 2 & etc. I'm kinda interested in learning the life of the CQC inventor

Also, if for spin off, maybe Kojima would want to do for Gray Fox as well? He's a badass I'll give you that!