Think it hasn't being officially dated yet. With 6 & 5 they were dated for release like 3 weeks before release, so I would imagine that is likely to happen here as well. I expect a September release though for this game - they won't want it too close to RE7 in January 2017, whilst they also have another RE title to announce (possible remaster?) which could come out later in the year. I kind of expect Capcom to release a port/remaster of Revelations in the winter months (fingers crossed)
As for this, I think it is most likely to be based on the PC's Ultimate HD edition. So it will just be a port of that most likely, so will benefit from a graphical and performance upgrade in comparison to the old console versions - nothing too exciting, but then from the cost of the rest - likely won't be a full price entry either (around $19)
Still hoping they release a physical bundle of 4, 5 & 6 here in the UK, since we didn't get the separate physical releases.
Edit - Confirmed for August 30th - I was nearly right
Good timing though. Details:
http://www.capcom-unity.com/timturi/blog/2016/07/07/resident-evil-4-arrives-on-ps4xbox-one-august-30