After the new client is completed, new software for the PC version will be distributed online, and can be acquired free of charge. Character data and progress for players already playing the PC version will also be preserved, allowing those players to continue using their in-game avatars. Another announcement will be made in the future as the day on which the new FINAL FANTASY XIV software will become available for download draws near, and the PlayStation®3 system version officially released.

This is a quote from the original post that also contained the road map download. It is still available for viewing on the Lodestone. There has never been any further details posted that I have seen. I suspect that they will make a download site available via the Account Management system with access tied to your FFXIV account. This part is just a guess on my part.