These 'new and improved' versions aren't. At least not in any significant, meaningful way. What you're seeing is the power tool equivalent of a car's midlife update - the 'facelift' which usually consists of 3 extra paint colours, a new front grille, fancy LED headlamps, and some different wheels. It's the auto industry's go-to method of boosting sales by convincing gullible buyers that 'this year's new revised and updated model' is somehow vastly superior to last year's.
The reduction in blade kerf from 2.2mm to 1.8mm (which Festool nonsensically claim will enable you to saw 'twice as fast') has probably been done largely to address the fact that they are losing significant numbers of sales to the Mafell MT55 (which coincidentally just happens to have a 1.8mm kerf - who would have believed it ?? [eek]) and which is considered by many people to be a much better saw - way more powerful, better motor technology, better engineered, much more robust, and with some clever features which are absent from the TS55. Their rail system also makes Festool's look a bit amateur-hour and home-made, if I'm being frank - although Mafell include an adaptor with their saw so it will run on Festool rails. As someone who owns both saws - I know which one I reach for almost all of the time. If you’re looking for a more powerful upgrade, the Mafell is worth seeking out to see if it meets your needs.
The TS55 is a truly, truly lovely saw. It cuts magnificently on the right material at the right thickness - and I absolutely love mine. It was a total game-changer when I bought it, it's still right up there in the overall plunge saw hierarchy, it's been utterly faultless, and it still performs as well as the day I bought it, despite the daily torture it's endured.
But it's underpowered in the extreme. Cutting 40-50mm hardwood one-pass is a total no-go, even using a super-slow feed rate and a 12-tooth Panther blade for rips. So for me - fitting kitchen hardwood and composite countertops virtually on a daily basis, whilst using a saw which constantly shuts down into limp mode after two feet of cut when I'm under pressure to bring jobs in on time and on budget - that just became a total deal-breaker. Reducing the blade kerf, whilst not addressing the ‘elephant in the room’ issue of a fundamental lack of motor power, is a golden opportunity missed by Festool IMO.
There's been a new king sitting on the throne for awhile. And he doesn't come in a grey-and-green case.