I can see the 321s lasting far more than 40 years total with this refurbishment.
The 315s had a very basic refurbishment which didn't change the traction package at all (apart from perhaps a bit of needed maintenance), and didn't really change the body in principle either, and by the time they'll be ousted from the GEML in favour of 345s they'll be up to 38 years old - the WA units may last longer depending on what the stock plan is for that route under TfL. With talk of them going onto the valley lines, they'll be running at 40+ on largely original equipment.
Meanwhile, the oldest 321s will be over 30 by the time they receive this refurbishment, and it's pretty extensive - wholesale interior replacement, traction package replacement too. If the basic refurb given the 315s in the mid 00s can see them run for a further 15 years +, the 321s should achieve at least 20 from this, possibly 25 - they are after all, now 'energy-efficient', air-conditioned and DDA compliant after these upgrades, so the only reason to replace them would be mechanical wear or some unforeseen shakeup of rail vehicles as a whole, provided the traction package provided proves reliable. If it's successful, I wouldn't be surprised to see 321s still about in the 2040s.
It's kind of a shame to see this is still going to be such a long time coming, two years before the second unit in service, or any change in traction package according to the article, and 6 years for full fleet conversion, though converting 94 units is understandably a slow process.
Lights may be changed, but I'm glad the light clusters are staying. Few seem to agree when I mention it but I think the 321 is actually one of the best looking BREL units of all - perhaps my opinion's tainted by familiarity
There's no getting around it, 3+2 seating
is cramped. Even with regular build passengers it does constrict your arms somewhat, and in winter people wearing coats makes it a really tight squeeze. For my <15 minute journey from Upminster to West Ham on a 357 every day, if there's only middle seats available I'm happy to stand. Were I going more than 20 minutes I'd probably take the seat, as I regularly do when travelling on a 321 from Liverpool Street to Shenfield. I've not really thought to evaluate which is more cramped in that scenario - it seems like the 357 possibly is slightly, but I doubt there's much in it. Not going as far out as Chelmsford and mostly travelling peak it's been a while since I've had to sit in a group of 3 on a 360, so I can't compare those.
Not changing the info displays is unsurprising and ultimately the right decision, but still a little disappointing imo. The existing ones do the job (so no reason to waste money changing them), but they do very much seem 'tacked on' on the existing units when compared to the natively installed units on Desiros and Electrostars (though the failure rate of the displays on the latter is terrible), and that feel is unlikely to change in the new interior I suspect. Could be worse, the 315 displays now being fitted are like cheap knockoffs even of the ones fitted to the 321s - right from new the text has been jittery and very blurry on the units I've seen it on.
Traction motor noise is kind of a pointless discussion, but up until relatively recently I'd branded AC traction sounds 'more interesting' primarily because of the non-linear relationship between speed and pitch. Latterly though I'm starting to admit I will miss the DC motor noise - when I was young it was 'the noise a train makes' and it will be odd for it to be missing from the railways in general. That said, modern AC motors are typically quiet at high speed - the traction motors currently fitted to 321s certainly are not. For the regular non-enthusiast passenger experience, it's an improvement.