First of all; I do not intend to insult you
You seem to have strong arguments for what you propose.
I don't know much about J.J's faroese ortography, other than something I read about it being purely phonetical.
Now, I can only think of an example from my own country to point out why this could be problematical.
A man who lived here in Norway in the end of the nineteenth century, called Olaus Fjørtoft, proposed a spelling directly based on the spoken language of the common people. This argument "fall på si eiga urimelegheit" as we say. There were simply to large differences in pronounciation across norway that such a spelling wouldn't be beneficent. Instead people stuck to I.Aasen's etymological spelling.
One thing that Fjørtoft was succsessful in though, was making writers of the landsmål(early nynorsk) drop unpronounced consonants.
This is still practised today, allthough not completely consistent. For example one writes 'leiar' for 'leidar'(leader) but spells 'huset' and 'tid' where /'hʉːse/ and /ti/
/ is commonly spoken.
I can't comment much on your criticism of J.J's work on norn, since I am not aquainted with it, but your theory that the old norse /á/ evolved into something else than scandinavian /ɔː/ is very interesting, and should be thuroughly discussed.
Do you know if old norse /í,ý/ turned into /ʊiːj/ on Shetland and/or Orkneys?
Maybe it would be good to have discussion on source criticism in the nynorn project.
But that's as far as my current knowledge strechtes, and so also my reply
Thanks for an interesting post!