My predictions are the following:
1) 24-28 MP (I would be really surprised if I see 36 MP).
2) 1-2 fps more than current 5DIII. In reality I think it will be 1 fps more. Canon definitely does not want to go to 7DII fps area

3) Built in GPS (this is simple feature which is not hard to include)
4) 4k (however, with some restrictions). If there is 4k, then CFast will be included as well.
5) Better AF - 65 focus points as in 7DII. What it would be really good to have wider spread of these points as in 1Dx
6) Better noise reduction, native iso still 25,600 (I do not think that Canon will match 1DxII specs in 5D4)
7) Anti-flickering, DPAF
8) Better weather sealing which will be similar to 7DII.
5DIV is the main working horse of many photographers. Also, it is a more affordable camera comparing to 1dXII. So, Canon wants to keep its current customers and wants to force them to change 5DII and 5DIII into 5DIV. There is a question what features are very important to wedding photographers, which would force upgrade. In my opinion, it is cleaner images in higher ISO and higher DR. Anti-flickering might be useful feature as well.
Also, I notice a trend that some wedding photographers are switching to mirrorless cameras (e.g. Sony). This trend is not very threatening, however, after 3-5 years when mirrorless will have siginificant improvements (I hope) in AF, OVF areas, quite many photographers might consider mirrorless rather than DSLR. Currently, I really expect very good financial year for Canon after launch of new 5DIV (especially if pricing is reasonable).