Bring OkamiHD to Xbox One

The browser for Xbox one will never have Plug-ins. In a few due time everything will be HTML5.

That's why I said or make an app for silverlight...

As always, it's up to the game publisher/developer to approach Microsoft to bring such a game to the platform. The fact that it runs via Silverlight has no bearing. Other than the browser plug-in, Microsoft itself isn't affiliated with this web based game.

When you release a game on a console you must pay that company a licensing fee, this can be quite a substantial amount of money.

Larger game makers have no problem with this but smaller studios must often pick which console to release on. That is more often than not going to be the one with the largest install base, that at this current time is the Playstation 4. Also bear in mind that
the console makers charge a fee for every patch released.

Any fees to release for the PC are far far smaller and there are no fees if the company wishes to patch the game.

In short. It's really expensive to release a game on a console and they had to pick the one that'd make them the most money.

Whatever platform a game developer decides to release their game on is solely up to them (or even their publisher).

You can try going to the
Grey Box website and ask them directly.