Part of the problem with Blake is that they didn't do many interesting things with him. The original concept was very quickly muddled once the Odin plot got explained. That took away the wish fulfilment idea, left Blake stranded as a less consequential character. Some writers tried to do things with him but the drift from a Billy Batson/Captain Marvel style towards a Clark Kent/Superman style was already there. By the time we get to Blake not being real I think the writers had totally lost the plot.
As a side issue if somebody wants to chart the retcons that have occurred with Blake I would love to see a clear summary because it all feels very muddled in my memory and whenever I try and remind myself by googling it I get more confused. In fact I seem to get it all straight and then it slips away like a dream.
We will see, I trust Waid, and I doubt he will mess with continuity. In fact part of his role on SHIElD seems to be to assert continuity choices from editorial.