Nope
Morrigan's child (who can be a simple child, not OBG) will be addressed if he exists. If not - then he won't. Bioware so far seem to stick to the approach "as little connection to previous games as possible". D.Gaider stated that something like OGB should be a player's choice and won't be pushed into faces of new players, since it has a strong connection to previous PC and new player won't have a sinle idea what OGB is
In the twitter they stated that the dead dalish is a main default. Hence the OGB will
As much as I agree with you on this I feel the need to nitpick.
Also Bioware long ago confirmed that the Morrigan's child would be addressed in the game, if applicable.
That last bit actually agrees with your statement about the OGB, but we have no idea if she had a normal child due to the whole epilogue debacle.
As for arguing about the default/canon:
For the books we'll never know, but we can speculate. (Oh, all the fun!) 
For the comic (which has a separate canon) we can sort of guess because of the annotations, but even that isn't entirely clear. (More speculation!) 
For DAI the default is everyone that could have died likely died except for the people that have epic plot armor (Leliana).
Your theory is wrong. If they were to go the canon way, then Hawke would have been a male, not a female.
I don't recall them ever stating what the default gender/class was for Hawke.