This makes no sense. Moffat works for BBC, they don't work for him. He can't possibly be the one making the decisions about what he's going to produce every year
Well he could on the grounds that, whilst the BBC can make
Doctor Who without him,
Sherlock is his (and of course Gattis') show and whether any more gets made is entirely down to keeping the two creators happy. Considering it's one of the BBC's biggest hits (and sells very well abroad) I think they'd be willing to accommodate a fair few whims.
After all, Who is also still successful under his watch and the series has survived a gap year before. If part of the terms of making more Sherlock was him staying on Who with a reduced workload there, they probably wouldn't be completely averse to the idea if it got them more Freeman and Cumberbatch.