When I bought the Witcher 1 and 2 here on GoG many years ago, they came with Steam keys as well. Rather nice, as I like the freedom to play on either, (mostly I like the steam cloud saves). Was thinking about finally picking up the Witcher 3 now that its finished with all the DLC and on sale. But I'm not seeing any reference to Steam keys on the page.....

Does it still come with one?

If not I understand, GoG has a heck of a lot more features and client/platform upgrades since then. Still I thought it was nice when they did that. Especially for their own games. Makes me wonder though.... If I buy a physical copy of Cyberpunk when it comes out, will it be a Steam key? or a GoG key?

You can redeem Steam versions of the games on GOG but I've never heard of GOG providing Steam keys. That makes no sense whatsoever.

Cyberpunk physical (if available) will have GOG keys, guaranteed.