There were two Metal Gear Solid games on Nintendo systems: Twins Snakes on the Gamecube and Ghost Babel on Gameboy Color. Also, the first two Metal Gears were ported to the Famicom in Japan. The NES got a crappy port of Metal Gear and a terrible non-canon sequel.
I think there is a greater probability of seeing MGS on a non-Sony system than seeing Smash Bros on a non-Nintendo system. Konami is a third party developer; Smash Bros has been made by Nintendo’s second-party developers sinse the begining and features characters trademarked by a first-party developer. This means there are only two ways Nintendo would allow their characters on another company’s system:
1. They abandon the hardware business altogether (SEGA).
2. They get tripped up by their own contracts.