A Pre-teen Pack

Your argument is very well thought out. I read it all the way through and find I do agree.  I was troubled that teens in the Sims 3 looked way too young to even think about driving a car, let alone learning how.  I do think the cutoff should be 13-15, though. 16 is the age here to be considered old enough to drive.  So, perhaps they can get a permit at 15, just days before they are to age up to an older teen, who in many ways is a YA or very close to being one.  But, yes most of the mood-swings do seem to occur at this earlier time.  Here in the USA, an 18-year-old can sign contracts and get married without parental consent. (As stated, they are just about YAs in their late teens.) In the 18th century (1700s for those who get confused), teens were considered adults. They said of my 6th times great-grandparents that all ten of their children made it to adulthood.

I would be pleased to have such a pack in my game.

I understand where you are heading, but I have to remind you that we already have 8 lifestages and out of those 8 only young adults and adults are not ultimately ignored. Just a reminder, we only got two kits for kids, with another one containing one outfit for kids and no kit for toddlers and infants. Kids, toddlers and infants got almost zero outfits and activities in latest EPs, with teens only being better, because for the game they are basically adults, so, they can wear all the adult outfits and do a lot of adult activities. And don't even let me start with elders.

With that said, I'd rather for Maxis and EA to concentrate on the lifestages we already have, than creating new one that, after the initial pack dedicated to them, will end ignored like the rest.

I don't want a younger teen, I want a preteen Lifestage to be introduced to the Sims franchise that goes to middle school, Also hots puberty and progress into likes and dislikes especially style wise which can change as they change into an adult like a kid they favorite was pink then preteen it can still be pink or change to red and as a teen it stays or change to black. Same thing style like from wearing sneakers as a preteen to wearing sandals as a teen, wearing a full bathing suit, to a bikini or shorts to show off abs lol. Maybe even change friends like your childhood friend have different values and grew apart as teens or y'all stayed best friends. 

also middle aged before elder

The problem is Sims 4 teens are indistinguishable from adults. I think the request for a "pre-teen" stage is primarily a reaction to the fact that Sims 4 teens are essentially adults and the jump from childhood to the adult-like teen age is jarringly unrealistic and disruptive in storytelling. In my main game, I've never aged up kids to teens because I can't overcome the poor implementation of teens in Sims 4. It's essentially transitioning from child to adult. It reminds me of the exclusion of toddlers when Sims 4 was first released. The fact that Sims 4 teens are essentially adults makes it seem like when Sims 4 was released they ran out of time to Actually create a teenage stage (like toddlers) and so just skipped it by calling the adult equivalents "teens." It's like going back to Sims 1 babies being Object like in Sims 4 until infants were released. It's a tragedy to see these types of issues where Sims 4 has less quality than Sims 2. 

For some simmers it was a primarily about teens looking like adults in this version of the game the Sims 4 other simmers like myself wanted a preteen Lifestage in the Sims 2 and 3 when the teens were acting like teens. Preteens I recognize as a Lifestage in between a child and teen and I want that implemented in the game. 

So I'll say here what I said in other preteen thread topics I would like the rainbow core that was put up for vote against the Goth core I really liked it for like it to be introduced with the preteen Lifestage but all the lifestages can have the cute rainbow CAS and BB like for ex. A fuzzy coat, fuzzy little back pack or crossbody bag, a labubu and fuzzy teddy bear keychain on belt.

Harajuku rainbow style with the tinsel hair clips and stickers on faces.

For BB I would like a Lisa Frank inspired like bedroom set, the bed, the dresser, the night stand, the desk, the Armoire, Like make it fun.

Also like sports and cars and game bedroom again the entire set.

And even a bathroom set. 

I very much question the players who can't distinguish the teens from young adult and adult sims in-game. Are they not very observant? The teens in sims 4 are quite easy for me to distinguish in-game. Perhaps it is because I know they have a more narrow shoulder build and female sims have smaller busts (unless you make them differently in CAS). 

I usually make my own pre-teen by viewing attention to the age bar. A child has 13 days on normal lifespan. I dress them to look like young kids at first and by day 6 or 7 days of their lifespan, I dress them to look like an older kid/preteen. Once the sim ages to a teen, they have 21 days on normal lifespan. I do the same as I did for the child lifestage and dress them to look very young teen for about 9 to 10 days. I then dress them to look like an older teen after that. You can adjust the timing if you play on short, long or even aging off.

I think introducing another lifestage at this point in a 10+ year old game is only going to introduce more severe bug issues. We already have very buggy infants and toddlers, so that is why I view it as a bad thing. Also think about the amount of money it would take to make a whole new lifestage do all the different interactions needed.