Nope, they've said there's only the one.
The amount of effort necessary to do the same level of detail for the entire period would be staggering... imagine having to trace and create characters for every significant noble in Germany for 150 years :excl:
Plus the added burden of basically all sources being in Japanese - a language none of us at Paradox speak. But if Sengoku sells good enough there's always the potential of an expansion/dlc which might cover more start dates.