Sherlock nods and gives a smile, though he's more distracted with watching John enjoy his cocoa then thinking about tracing tracks in the snow.

"That would be ... fine." As long as there isn't too many people about to overwhelm every sense of reality. He can't leave London, though sometimes he finds all of the crowds milling about overwhelming. Fine. He doesn't know if that's the right word, for it either?

Nice seems like he's placating or appeasing John.