The Metal Gear Solid games span across decades, though not in chronological order. This should clear the timeline up.
While there's been no confirmation of a Metal Gear Solid 6 on the horizon, it seems unlikely that Japanese entertainment giant Konami would abandon one of its most beloved properties so easily.
It coincides with the release of Steam Trading Card and Badges support, though this isn’t unlocked via the patch itself. Metal Gear Solid 2: Sons of Liberty is perhaps getting the most changes.
With Metal Gear Solid Delta Snake Eater nowhere to be seen, eyes are turning to the also-missing Production Hotline series.