I don't think the 5D3 will be split into two different models.
Splitting it up increases the risk of both models where consumers may not be satisfied with both and even if they are satisfied with one of the models, there can be a big loss financially on the second if it doesn't satisfy the market. It also creates confusion in market, which model would be suitable. Eg. Someone who primarily wants photo use but also needs good video usage, which one would they buy if the 5D series is split up.
Canon make their money on a model that repeatedly gets purchased time and time again over its life span. Eg. 5D2 has been one of the best selling cameras of all time. Canon have had this camera on the production line time and time again.
I think Canon should make their necessary changes such as MP increase, ST-E2 transmitter, AF focus points, Digic 5+, 3.2" clear view II screen, increased weather sealing etc.
With these changes, the 5D3 will sell itself.