Yes, it's perfectly logical to expect a union between Morrigan and the Warden to produce a qunari baby.
A Dwarven Warden mates with a Human Witch to produce a Qunari infant....... *backs away*
How many years have pasted between the DR and now ?
Approximately 10 years and 4 months. OGB, if in existance, is now a roughly 10yo boy. Fear him.
OGB is probably spirit that uses the Inquisitor as a host. But seriously, I'm not sure how Bioware will address that OGB issue with different wardens unless they decided Morrigan slept with another Warden that we don't know.
A dev already stated that the OGB will not appear in Inquisition, beyond a few statements. Beyond that? Only the Maker can say for sure.