Thanks for writing all that up, I really appreciate it. I remember reading some other theory (I wish I could remember the author) that stated a similar theory to Oosthuizen, which is that some form of embryonic precursor to Old English was introduced to Britain by the Belgae before the Romans even arrived, and that it followed a similar trajectory to the one you suggest. It lied in wait, evolved as a trade language, and then erupted across Britain as North Sea trade overtook Channel trade, eventually becoming the primary language of the mercantile class before spreading both upwards and downwards to the elites and the peasants, respectively. What's strange though is that if it was a trade language, why did it only emerge and gain traction in Britain, and not across the entire North Sea?