I found an interview with Phillippa Gregory in which she states:
"In terms of styles of language‚ I deliberately took the choice to use fundamentally modern language‚ but quite pure and quite simple. So I don′t use slang and I don′t use modern idioms. This is to make it acceptable to a wider audience and to write as well as I possibly can without being limited by language. For example‚ if I was to write a novel set in France and there were French people speaking French to each other − I wouldn′t put that on the page in French‚ I′d put it in English − and the reader understands as it′s part of a convention of reading a novel‚ that when someone is speaking Russian or French you don′t get a page of Russian or French − you get it in English.
If someone said to me that the past is a foreign country‚ it seems to me that it speaks a foreign language. So in terms of any notion of thee and thus and thy‚ superfluous words‚ I tend not to use them as it′s so strange to the modern eye. You also gain nothing by using them and the chances of rendering them correctly are very slim.
In the case of early modern society we don′t know how they spoke‚ we know how people have written down Shakespeare plays‚ but we don′t know how people actually spoke or what they sounded like. We do believe however that Anne Boleyn maintained the French accent throughout her life as she believed that it made her a bit special‚ I mention this in the novel. But in terms of how actually people spoke‚ we don′t know‚ so I won′t even make a guess."
An author who thinks differently is Patricia Finney. I once tried her book Firedrake's Eye but didn't get very far with it as I found reading it was rather more of a struggle than a pleasure. A review of her book A Shadow of Gulls says she "endows her players with a rich language--essentially modern English lightly laced with fanciful syntax and Elizabethan vocabulary."
On Nov 26, 2003 Roz Kaveney wrote in the Telegraph : "The books' language is a triumph. Finney finds a workable compromise between anachronistic slanginess and a verbose rhodomontade that would probably more accurately represent much of Elizabethan speech."
Now rhodomontade is not in my trusty dictionary, but rhodo means rose coloured. However, the internet tells me it means "pretentiously boastful or bragging." Still, it doesn't tempt me to go find the book and read it. Would you?