The Wikipedia article on "T-V distinction" linked to an article by Dallin H. Oaks from the May 1993 Ensign entitle The Language of Prayer, in which he counselled Latter-day Saints to use "the dignified but uncommon words like thee, thou, and thy" which are "appropriate to symbolize respect, closeness, and reverence for the one being addressed".
He also quotes several prayers in translations of the scripture or spoken by latter-day prophets (for example, in Doctrine and Covenants), which use "thou" and "thee", and seems to imply that the use of those pronouns in English prayer is due to "divine commands or inspired counsel".
I'm a bit bemused by that article, the emphasis on specific pronouns for English, and the quotations from other leaders to similar effect (e.g. President Kimball quoted as saying, "In all our prayers, it is well to use the pronouns thee, thou, thy, and thine instead of you, your, and yours inasmuch as they have come to indicate respect"); it seems to be taking an artefact of an archaicising translation and turning it into doctrine. (Though the article claims, of course, that the counsel to use those forms is "much more than an artifact of the translation of the scriptures into English. Its use serves an important, current purpose.")
I also wonder whether the article was intended to have any implications for other languages—especially when Elder Oaks says that "Some languages have intimate or familiar pronouns and verbs used only in addressing family and very close friends. Other languages havehonorific forms of address that signify great respect, such as words used only when speaking to a king or other person of high rank. Both of these kinds of special words are appropriately used in offering prayers in other languages because they communicate the desired feelings of love, respect, reverence, or closeness."
What is it to be, then? Informal "T" words, or formal "V" words? Doesn't saying that either of those are fine (depending the specific language) subvert the point that English-speakers "should" pray with certain pronouns?
Especially given the history: God was addressed with "thou" specifically *not* to use a respectful pronoun, but an intimate one, to show closeness to one's Heavenly Father. Using a now-unusual word would seem to subvert that, making prayer feel more distant and less like talking to an intimate friend or a parent.
And then he says that "I am sure that our Heavenly Father, who loves all of his children, hears and answers all prayers, however phrased. If he is offended inconnection with prayers, it is likely to be by their absence, not their phraseology."
...and goes on to say that "as we gain experience as members of The Church of Jesus Christ ofLatter-day Saints, we need to become more mature in all of our efforts,including our prayers" and mentions that "Men and women who wish to show respect will take the time to learn the special language of prayer. Persons spend many hours mastering communication skills in other mediums, such as poetry or prose, vocal or instrumental music, and even the language of access to computers."
Bzuh? I thought prayer was about communing with your father in heaven, not some kind of stylised contest like Japanese calligraphy? Why the emphasis on form?
I'm also not really convinced that "the manner of addressing our Heavenly Father in prayer is at least as important as these," nor of "the importance of using this reverent and loving language".
I pray that way because it's the way I heard my father pray while I grew up (and because I've had enough exposure to such prayers, and to scriptures written in archaicising language, that I'm fairly familiar with the special verb forms associated with the pronoun "thou" so they don't require much effort)—but I've always taken it as a tradition, or an in-group thing, rather than The One True Way to Pray, or something vital and important, let alone something "based on modern revelations and the teachings [...] of modern prophets".
I don't know.
Edit: Apparently, that was a talk at General Conference.
I wonder what they made of it when they translated it....
(Especially: whether they bothered to include it at all, since it's relevant—on the surface—only to English speakers; whether they included it but kept the message about English; or whether they applied the principles to the target language, e.g. counselling German speakers to use "dignified" Sie or Dutch speakers to use jij for "love and closeness".)