I see nothing inherently wrong with the S650 platform or the current engines and transmissions.  Who has something objectively better?  Sounds like you just want change for change’s sake.  And where are these other non luxury sports sedans?

Has to be Flat Rock.

If not Flat Rock, where will they build this 4 door Mustang?

A hybrid Mustang sedan would make lots of sense since it could offer AWD then 

That was apparently a mustang hybrid. 

Same outfit, though the fire apparatus chassis business was spun off.

I wonder if this is the rumored Flat Rock vehicle?

How much do you really need in ICE development? The current engines can carry Ford with minor updates till middle of next decade. CAFE might see a pause of 4-8 years but all it takes is some sort of oil shock to drive prices up and with cell pricing dropping and getting better, automakers will want to go the EV route because they are cheaper overall then ICE products to build and develop.    The Mustang sedan isn’t going to be a huge player in the market sales wise-they’ll be lucky to sell maybe 50k of them a year-it helps ford with CAFE and profit. 

My main concerns: 1. The Mustang is already on re-re-revamped bones, and is likely to suffer in comparisons to more recently engineered sport sedans. 2. With the nebulous nature of the EV market, are there scraps in the budget to keep some ICE R&D going? The various engines across the board have been almost stagnant (minus the Dark Horse 5.0). The turbo 4s are seemingly forgotten, the V6s are far from class leading...yeah, I have concerns. 3. Dilution is an obvious twitch. The MACH-E didn't phase me, with EVs being literally legislated in many markets...but, a Mustang sedan can NOT be a Lincoln LS-esque "shoot for the middle of the market" gaffe.

Are you messing with us? My heart can't take it lol. If if is s650 based, does that mean it's gonna use a lot of the same sheet metal, just extended, or is it gonna be a completely new top hat riding on the s650 platform with its own unique styling?    I didn't think s650 could be stretched to handle a 4 door but I'm pleasantly surprised.