I have many concerns about this, not the least of which is the pressure it could put kids under to lie on the application to skirt this "requirement". I know my daughter feels she can perform the duties necessary, and she has been working on her conditioning, but the BMI is a very out-dated and poor reflection of physical conditioning and still shows she is morbidly obese, when, not to be too revealing or inappropriate, she is a 5'4" and a 32 triple F bust size and probably carries around enough weight in her breasts to push her over the BMI limits regardless of her actual body fat content. She did the right thing and indicated that according to their standard she is obese, and that is probably accurate in any case, but she was very tempted to tweak the numbers to avoid this as an issue and delay her going on her mission.
When I went on my mission, also in 1989 (not sure if colton wants this to get out, or even remembers, but we went into the MTC at the same time going to the same mission, but in different MTC districts), I was definitely overweight, at just under 6'2" and about 280 lbs. I came home at nearly 6'3" and 215 pounds, so physically the mission did me good. But even at my weight beforehand I had always been in pretty good shape, having played 3 sports and still remaining very active in basketball and other sports (played competitive racquetball for a while), so I had no problem keeping up, but I would definitely not have met the "specs" to go on the current application form.
I also can understand wanting to raise the bar, and ideally that would be the case that kids are preparing for their mission from the time they are 16. But I know from my own experience, and now with 3 of my kids having moved through these years, that this is a rough time for kids. Things change rapidly. Their hormonal changes can spur great changes in attitude, behavior, feelings, everything. I didn't make the decision to go until the month before I put in my papers. My daughter wanted to go, but had a high school sweetheart that she thought she would marry, so she had her mind and heart set on that first, a mission second. Now it worked out differently and she wants to serve a mission, but isn't as prepared as she could have been. Some of the best missionaries I knew were last-second deciders. I just wonder how many kids they are alienating if they make this process any more difficult.
But I guess that is another good question, should it be difficult, at the risk of pushing some kids away. Is "losing" some kids worth it to make sure the kids that go are the best they can be? Is it a winnowing process in which the ones who just "can't hang" are weeded out so they don't taint the field later?
Seems counter to the mission of the church to me, which most succinctly stated would be "to bring about the immortality and eternal life of man". Wouldn't that mean equal opportunity for all, and not just those that are lucky enough to be in good shape, or are able to get things straight for themselves years ahead of time during what for most kids is a pretty chaotic time in their lives? I find that just a little disturbing. Admissions requirements for BYU is one thing, space is limited. The church has neither limited space, nor limited funds when it comes right down to it, when it comes to missionary service, and anyone who feels the spirit prompt them to serve should be given that chance, shouldn't they? Regardless of concerns about financial liability.
Either it is governed by revelation, both personal and by proxy say through a bishop, or it is regulated by regulations. I don't see the 2 coexisting very harmoniously when the decision is such a personal thing and not some over-arching canonical teaching.