Unfortunately, this proposed idea pushes toward making very big profiles that contain heavy "contractual" roleplay information, and otherwise "clinical explanations" about the character which aren't very fun to read, like we see on other RP sites. These subjects on profiles can be very intimidating, and some of us suspect may not actually be helpful for facilitating new roleplays.
The whole problem with this kind of thinking is that whole feature is supposed to make it all lighter, not seem mandatory and overall avoid problems you list here. It doesn't encourage, and honestly, expecting people to suddenly stop developing characters is naive at best. Plus, if you think that forcing people into something they speak against is excused by some idealistic dreams of being community-changer... well, it will sooner kill any community than help it.
The concept of stat sheets, though, is somewhat outmoded in my opinion. Unless one is playing a 'stat' based game, in which a centralized (gm) figure requires those stats to be on hand, it seems much more fulfilling to allow them to be discovered either through play, or through some form of written prose. Far too often, when I have played on other sites, other players would mysteriously know things about my character, such as his favorite food to give him in a completely random gift. That was what came of a stat sheet.
Simplifying everything to a concept of stat sheet is picking one thing you don't like about the suggestion and basing whole argument on it is not entirely constructive discussion. We are talking about any kind of information that is relevant, and stat sheet is a tiny subset of possibilities. On a sidenote - there is a Game System trait that defines RPG system character was created for which immediately makes stat sheets have sense. Is just the fact that it is not filled.
Perhaps one can take their character and stick he or she into a random situation, taking the time to describe physical appearance, glimpses of personality, and maybe even a smattering of background. Most of those details, though, particularly anything that is not a physical appearance, should be encouraged to come out through play, instead. If one wants to learn why a character fears the dark, or why a character avoids sweets, perhaps they should ask or make observations through the course of play.
Having visual description be explicit can help people who get into roleplay - they can cherry pick visible details and incorporate them into the posts. We are supposedly in a site where people know how to write and how not to use information they shouldn't have, at least without properly constructed explanation. If we have it all shown through playing with somebody only, that is limiting the other player.
There is a lot of details that could be highly usable by another person but takes too much words to be a good story, and is not confidential enough to be like "not allowed to be know by anybody unless explicitly told ever".
From my perspective, while I like how neat collapses can make a profile look, I would honestly rather see players working to lay out the important information in story format. From my understanding of the site, one of the core concepts is to inspire literature style writing. Maybe we can encourage players to write short stories about their characters, rather than lay things out in a stat sheet format?
Look at my profile - can you imagine how long a competent story describing all of that would be, and how that, instead of a bit of text on profile, unread would be? I would rather have a few blocks of text like that neatly organised than sit and be 'encouraged' to pour hours and hours into writing stories just to show some information another character playing with mine can have in some way.