To some extent this is a promising development:
However, this doesn't necessarily work to the advantage of evangelicalism. It's not as if a loss for the LDS church is a pick-up for the evangelical church.
For one thing, a lot of Mormons seem to be defecting from the LDS church for some of the same or similar reasons as people defect from evangelicalism. Offended by social conservatism. Objections to the historicity of scripture. The challenge of evolition.
Superficially speaking, there are parallel issues. So ex-Mormons might consider defenses of biblical inerrancy to be special pleading. Too much like what they already encountered in Mormon apologetics.
One thing I'd point out is that the comparison is very misleading. The Bible was written roughly between 2000 and 3500 years ago–depending on when you date the Exodus. By contrast, the Mormon "scriptures" are 19C literature.
Arguments for the intermitant obscurity of the Bible, textual transmission, &c., don't carry over to 19C documents. At this distance in time and place, there are bound to be things about the Bible that we don't understand very well. Likewise, textual transmission is more complex.
The same excuse does not apply to 19C literature. We know that period very well. We know a lot about Joseph Smith and Brigham Young. It happened in our own backyard. Recent history.
Of course, the Mormon "scriptures" claim to recount the distant past, but these aren't ancient writings about antiquity. The allowances we ought to make for the Bible are not analogous to newly-minted literature.