Ditto JBJ's comment...there's just no more room. Something to consider is how much space guests WANT to put their own things out. I have guests who bring framed photographs of their family with them.
What you would probably want is a pre-measured pouch so guests didn't overfill the coffee machine. Hotels have this. You can buy them by the boxful.
Another consideration for me is that if they have coffee in the room, they'll never come for breakfast! It's the coffee that lures them out...
I know I'm not supposed to decide for guests what they do and don't do while they are here, but...early morning coffee in the kitchen with hubs is a BIG part of the allure. It's one of the biggest comments we get here...the conversations over coffee. If guests had coffee in their rooms and only came at 9:30 to eat, they'd miss all of that. There are guests who just sit there and take it all in for a couple of days before they join in. But, that they ARE there each morning LOOKING for the conversation means it has meaning for them. (Sometimes they even ask, 'Where's that guy from yesterday, the one with the race car?')
We are perfectly ok if you take your coffee to your room to enjoy quietly, we don't care if you come out in your jammies, teeth unbrushed and hair standing on end to get the coffee, but you're missing a lot if you don't hang around.