I haven't read the Atoms of Language but this sounds plausible and is if I remember correctly, more or less, what is believed to have happened. The diachronic study of english from say 900 to 1300, shows a language undergoing drastic changes such as the loss of inflections, grammatical gender, and adoption of north germanic (danish) words and later norman french ones. The idea is that original SOV speakers of saxon were put under the heavy influence of the SVO languages of the danes and later (post 1066 - battle of hastings) that of the SVO normans. It would make sense, especially since even OE was not a truly pure SOV language and allowed a much freer word order due to the inflection system, which upon dying out forced word order to take on a much stricter form.
As an interesting side note to show just how big of a hack mixed up jumble of everything modern english is, the usage of the verb do, in elliptical sentences and questions such as "do you want some coffee?", is very rare in indo-european languages (only found in celtic langs such as irish) and thought to have been picked up during the time in which saxon speakers and celts were sharing the same island.
I find this proposal an interesting thought experiment, for sure, but replacing all the vocabulary except the grammatical words seems more likely to me than replacing just the grammatical words and the grammar and retaining all the other vocabulary. Are there any other cases of the grammatical words being replaced while the rest of the vocab was left intact?
The fact that there was so much and such dramatic change happening that either of those possibilities are reasonable suggests to me that we're not going to get a definitive conclusion anytime soon.
As an interesting side note to show just how big of a hack mixed up jumble of everything modern english is, the usage of the verb do, in elliptical sentences and questions such as "do you want some coffee?", is very rare in indo-european languages (only found in celtic langs such as irish) and thought to have been picked up during the time in which saxon speakers and celts were sharing the same island.