For some time now, the matter of classical versus modern writing has weighed heavily in the discussion of my mind-congress. Here is my thought: given the sheer reverence that is given to classical pieces of writing by large associations, I, as a high school student in the United States, have been exposed largely to this style. However, over time, I have come to realize that often times, though it may be by artistic choice, many lapses in syntax and diction can be found in classical literature and prose. And do not misunderstand me; I value and appreciate classical pieces and revere them as many are masterpieces. But, given the advancement and rigor of the education of the English language to those who may pursue it here in the States, would an aspiring writer such as myself utilize that literacy to craft new styles, or attempt to replicate the styles of the 17th and 18th centuries, but still with personality?
Centuries don't have styles; writers have styles. True, there are certain broad features of the way things are written which change over time, but they are very much secondary to the styles of individual authors. And diction and vocabulary are only a small part of what constitutes an author's style. Austen's cool ironic detachment is a much a hallmark of her style as her diction and vocabulary, and you certainly would not mistake her for any of the Brontes.
Nor would you mistake writers of the 17th century from those of the 18th or those of the 18th from those of the 19th, etc. There is a marked development of fashion in literature from one centry to another, which continues into the 21st. These fashions have as much to do with weltanschauung as they do with the use of language. The relationship between character, narrator, and reader, for instance, is a far more distinctive part of the evolution of storytelling fashion over the course of the 20th century, reflective of a larger social trend of descent from confidence into doubt about the reliability and objectivity of human judgements.
A writer today who wanted to emulate Austen would come closer to their intended effect if they focused on emulating her confidence, irony, and wit, than if they focused on her diction and vocabulary. Indeed, the effect would be far more convincing with the former focus than the latter. Imitation of the diction and vocabulary without the fundamental authorial stance will sound like a painful pastiche, almost mockery.
The key stylistic fashion of the later 20th and early 21st century literature has nothing to do with vocabulary and diction. It is the withdrawal of the authorial voice; the refusal of the author to speak directly to the reader in any manner. Partly this is the influence of the movies at work, and partly it is our artistic lack of confidence showing through. It is the author's voice shining through, more than anything else, that strikes us as foreign about the classics of the modern era.
You should only attempt the style of the 17th/18th centuries if you're writing some kind of pastiche or mimicry of a book written then — for example, a Sense and Sensibility and Dragons kind of thing. CE Murphy did a reworking of Pride and Prejudice and added magic to it, using a style similar to Austen's but without strangling herself with her own sentences.
However, modern readers can find this convoluted structure and stately diction hard to follow, so I wouldn't try to replicate it precisely. Approach it, but aim for clarity.
And honestly, if you do use this kind of style, be aware that it's a gimmick, and treat it accordingly. It will narrow your audience. You may find a deep niche audience (readers who love Regency romances, for example), and devoted niche readers are not to be taken lightly, but that kind of writing will not get you broad acclaim or sales.