The english translation of the post reads as follows:
“Silent Hill is in closed room setting and doesn’t require full action so that we can focus on the graphic quality. Enemy doesn’t have to be a lot or move fast. It only requires scariness by graphics and presentation. As being a creator making action game in open world, such game is very enviously attractive. Wish someone could create this on FOX engine.”
Considering Kojima has been willing to lend his talents and resources to other Konami published franchises in the past (see Castlevania: Lords of Shadow) his involvement in a Silent Hill title isn't all that farfetched. Whether or not this tweet will prove to be anything more than just Kojima expressing his opinion remains to be seen, but it certainly does make you wonder about the possibilities.