If we are still going by the whole "game a year deal" 2.5 would be next, and maybe if we get REALLY lucky KH3 in 2015.
Versus XIII's preorder page was open for seven years before they closed it then reopened it as XV. There is an Agni's Philosophy preorder page despite the fact the tech demo has been repeatedly confirmed to be just a tech demo.
They put preorder pages up for anything, as long as it exists (sometimes even if it doesn't exist)
Nomura has had the plot planned since before BBS, but I think KH3D and their cancelled KH game put something of a wrench in his plans. Whatever he had envisioned in the past is probably very different now, so I wouldn't doubt that they are still ironing out the creative things while they work on the assets.
Actually they are still waiting for Versus