What Marti said. The biggest thing you can do to support a game is arguably to promote it and encourage the exponential/sustainable growth of the playerbase.
Also as a quick glance, I just looked at one of KSI's Q&A videos (the one with his (ex)gf I think). It has over 18 million views, which is even more than [edit: some] FIFA World Cup games. If you're that popular and are guaranteeing millions of views on your channel, you're basically in line with top TV shows in terms of views, and I don't think it's wrong that popular youtubers are paid to the same standard, especially when you factor in that in a game like Minecraft it would be hard to constantly come up with new content as often as they do. In the Minecraft-specific example, you're technically directly contributing back to the game by buying the client itself, and many contribute to the community by purchasing subscriptions to servers like mineplex and so on (also related to streaming: if mojang didn't want people to stream Minecraft, they wouldn't have included an inbuilt twitch broadcaster).
And while I don't think anyone would make money from streaming AC (unless their channel already has a bunch of dedicated followers who just watch every video you produce, there was a russian dota 2 player who was streaming q3cpma on his channel and it had 12000 viewers, which is 1000 times the magnitude of the game's actual playerbase), if they ever did make a bunch of money from a game which offers everything totally for free, I'd consider it a little unethical if they didn't at least donate something back.
Also as a quick glance, I just looked at one of KSI's Q&A videos (the one with his (ex)gf I think). It has over 18 million views, which is even more than [edit: some] FIFA World Cup games. If you're that popular and are guaranteeing millions of views on your channel, you're basically in line with top TV shows in terms of views, and I don't think it's wrong that popular youtubers are paid to the same standard, especially when you factor in that in a game like Minecraft it would be hard to constantly come up with new content as often as they do. In the Minecraft-specific example, you're technically directly contributing back to the game by buying the client itself, and many contribute to the community by purchasing subscriptions to servers like mineplex and so on (also related to streaming: if mojang didn't want people to stream Minecraft, they wouldn't have included an inbuilt twitch broadcaster).
And while I don't think anyone would make money from streaming AC (unless their channel already has a bunch of dedicated followers who just watch every video you produce, there was a russian dota 2 player who was streaming q3cpma on his channel and it had 12000 viewers, which is 1000 times the magnitude of the game's actual playerbase), if they ever did make a bunch of money from a game which offers everything totally for free, I'd consider it a little unethical if they didn't at least donate something back.