The sailing skill would be almost pointless and have no real place in the game. Think about it.
Again, it doesn't have to be all about travelling from A to B, RuneScape has ended up in a design where people have forgotten that the slightly damp area between two points on land actually exists on the map. People will realise how big distances actually are when they can't teleport to get somewhere, especially when there's storms, pirates, shipwrecks, islands and sea monsters located somewhere between A and B.
At the moment, I'm still a serious skeptic about whether it will actually happen in the near future, but it is true that the concept could be made into a full skill. When you have to beat firemaking in terms of imagination and complexity, it's not that hard to make an acceptable plan for it.
Jagex has demonstrated their ability with Java, they can make Randomly Generated Scenarios (SC), they can make customised structures (POHs), they're ridiculously creative (a lot of things).
Jagex can do this effectively, but I don't think they will quite yet, there's Upgrade Year to deal with. I think that's a fairly convincing bit of evidence that Jagex has no intention to release something so new, so big and so different as the Sailing skill this year.