All interesting stuff. However, can I play devils advocate for a bit.....
What if I were to suggest that the syllabus should contain the bare minimum neeed to fly safely. Basic handling, circuits (including crosswind), emergencies (lots of them), navigation without navaids as per the current syllabus. Let's throw in some kind of escape from IMC, too, although I'm not sure how useful that really is.
I'm sure there are lots of gasps in response to this. What about navaids? GPS? Different types of aircraft? FADEC, Rotax engines? International flight? And so on, and so on.....
Well, the simple fact is that most PPLs will want some of these "extras", but very few will want all of them. And there's a reasonable chance that they won't be wanted immediately after gaining the PPL - there may be a gap of a few years in between. So why not have some system where all of these really useful techniques can be taught after a pilot has gained his PPL, perhaps a considerable amount of time after, when he is actually ready to use the information? You want to fly a DA40? We'll teach you about FADEC and glass cockpits then. You want to fly to France? We'll teach you how to file a flight plan and check customs requirements. You want to fly a Tiger Moth out of a strip in Yorkshire? Well then FADEC, glass cockpits and going to France are probably not subjects that you have much interest in learning......
Just a thought.
(Of course thoughts don't come from nowhere. This describes exactly what I did. I learnt how to file a flight plan from an instructor when I did a cross-channel checkout some time after getting my PPL. I learnt about glass cockpits when I first flew an aircraft with one. I learnt about Rotax engines when I first flew an aircraft with one, and I've never yet flown an aircfraft with FADEC so I know very little about it - and I'm not bothered by that, because I know that if/when I ever fly such an aircraft I'll learn all I need to know, and it'll be a lot more meaningful than it would have been if I'd learnt it several years ago.)
FFF
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(Edit to add that, contrary to some earlier posts, spin training, including demonstrating a spin recovery, is a mandatory part of instructor training - or at least it was in the UK when I did my instructor training, I don't know about other countries or about further back in time. It's also a mandatory part of renewal or revalidation of an instructor rating, every 3 years - at the very least, to brief the recovery, if the aircraft being used for the test isn't approved for spinning.)