I have been thinking about this: in Brazil, whose language is Portuguese, many Bibles use too formal language and uncommon pronouns, conjugations and adjectives; could this interfere on the people's interest on the Bible? Or could this be a barrier for their reading?
To answer your questions more directly, yes, highly-formal language can be a barrier to those who aren't as familiar with it. Again using the example of the KJV, it is contemporary with the works of William Shakespeare. Some can read both Shakespeare and the KJV with ease, understanding the more archaic words and phrases as written. Others, who may not have done so well in high school English, can read modern translations with ease, but struggle with the English of the early 1600's.
If the goal is to get people to read the word of God, then a translation in "their" language is best. Forcing a Bible-newcomer to read only the KJV is, in my view, insensitive and unwise, if the person doesn't grasp it
easily. Give the people the truth in simpler language first, and let those who are so inclined move to a more formal translation later. The New Testament was written in koine (everyday) Greek, not classical Greek... for good reason.