According to an official document disclosed by Konami during a briefing with financial investors, Metal Gear Solid V: The Phantom Pain is slotted in for a tentative "2015" release. Effort is being made to pinpoint its release more exactly.
Although, at the moment, that report has not been officially confirmed by the company, it seems that its launch window could be slightly slipped, because there are some problems with the Chinese localization, some bug-test undergoing and much more, as reported by GamingBolt. But according to a NeoGAF user it could be anticipated to Apr-June this year, because some other financial documents from other countries reported the game will be launched in Q1 (for Konami, Q1 is from April to June). It should be noted that both the user and Gamingbolt appears to have misinterpreted the original document where the game appears under the header Q3 releases / pipeline - the Q3 releases part of the header refers to games released during Konami's third quarter last year (Oct-Dec), not the upcoming releases in that list.
Here's hoping official information arrives soon.