I was under the impression that after the Jason Crump incident, leathers was going to be made mandatory in all FIM speedway meetings, but maybe the FIM has wimped out.
Everyone knows that leather offers much more protection in all types of crashes.
With the modern leather suits, (and I'm using road racing 2 piece set with the knee pucks removed at no extra cost by the manufacturer) and with stretch patches at bottom of back, behind the knee's, and over shoulders etc, movement is not the problem it used to be with the old style one piece suit.
It is easy to still get a full set of body armour and a good quality back protector on underneath modern leathers, and still be able to move freely.
I know cos I wear just this when I ride in the British veterans speedway meeting at Lydd.
I have looked closely at both Kevlar's & nylon, and there is no way I would race in either, a good modern 2 piece leather suit with full body armour underneath should be compulsory in speedway, and my leathers & armour was actually several hundred pounds cheaper than kevlars, but just my own opine, however, just to back this up, I had a pretty decent off at Lydd and at Rye House last year, sure the leathers got scuffed, but I walked away each time, absolutely no friction burns (but there never was when I raced in leathers in the 1980'e either), and no rips in my leathers.
Just a quick sponge down when I got home, and a light coating of baby oil on them and ready to go again.
No, it's leather every time as far as I'm concerned boy's, and I know of other speedway riders who are now going back to leather after years of getting banged up in nylon & Kevlar..!