A key that will send you wherever the Publisher and Distribution platforms allow for. Look at Humble for an easy example, a bunch of their games provide keys that will work on Steam, Epic, GOG, and even direct download if the publisher/developer has the servers for it. It doesn’t keep any one captive.
Haha, beat me to it. They are both a bit right, and these questions have been hammered out by game designers for years with no definitive answers in sight.
I figure, so long as the design was purely for the “artistic intent/integrity” of the game and not to manipulate players into spending more money, the rest can just be left up to each player to pick whatever game suits their fancy. Mass grind, no grind, or Tony Hawks Pro-Skater grind.