Well, I don't know if foils are developing so much, if pure race kites are not included. And their "development" comes from simple fact: they have bigger AR and higher cell count than kites used to have.
Speed3 was already very good kite 6 years ago and since then FS is mainly tweaked details. One earlier invention and Flysurfer specialty, jet flaps, is ditched even though it has sound aerodynamical basis. I'm afraid there is cost factor there. And same thoughts for rigid foil LE's, they were tested for Speed4, but found out not beneficial enough then - now they are used, even with higher number of ribs. There is no aerodynamical reason why rigid foils are needed for Speed5 but were not for Speed4.
So, no new technology but picking up good combination of available options, both for performance and costs. Perhaps Speed6 will have miniribs? They were tested for Speed4, but not used then and not used now. Heavyer fabric for Speed5 is not going forward either, but better cell billow control is - if it isn't just hype for new kite. No doubt about it, Speed5 looks very clean wing
Cell count (41 vs 39) is a bit higher like AR (6.1 vs 5.8 ), again small changes. Cell width/height is very close the same than earlier models.
Bridles and speedsystem have not changed essentially, what I could see from the video. Current 1:2:4 mixer was first used in P3, ten years ago. Bit early to comment more, FS hasn't published lineplan for Speed5 yet.
I'm not saying that Speed5 is not better kite than Speed4 and Speed4 is not better than Speed3. No, I'm sure newer models are better than old, but development is not radical. Speed series kites have been good for a long time. Good times for second hand Speed buyers
, even better if FS didn't have it's known problems with bridles