the whole round and round, devil take the hindmost and flashing light thing is totally out of Logan's Run.  RENEW, RENEW

Maybe motorbikes or some other elements of rollerball ?

Scything blades on the wheel hubs like Boudicca's chariot?

Nice

how about Mariokarts banana skins, grenades, oil squirts etc

Maybe giant flippers on the outer wall, like on a pinball machine ?

Brilliant. The guy knocked out gets the controller for the next lap.

big ramps with conveyors suddenly appear ahead with up or down conveyors.

A drop off in the middle to a volcanic lava lake

So, basically a mashup of cycling, Tron, pinball, Logan's run, rollerball and Mario kart. Could work...

Danish riders fired out of cannons

Have we missed anything? What about people in the crowd with high powered lasers. 

Strobe lighting

Crocodiles and lions let loose into the track

I'm going full Circus Maximus now. 

A man in a helmet with a net and a trident standing at the finish line.

A loop the loop.

Would still be less confusing than the rules for the omnium points race

Jumps with points for air but a hungry Terradactyl circling in the airspace above the jump.

a tunnel with a shortcut to the finish, but with snakes.

HGVs turning left.

Heh.

How could it be improved? I think giving riders a chain mace / morning star would be good. 

Mushrooms and banana skins.

(Not in the Hotblack sense)

"Mushrooms....Not in the Hotblack sense"

But now you mention it...

Also, cans of mace rather than chain mace

They should do it on BMX bikes with tasers on the handlebars

Two races similtaneously, one clockwise, one counter-clockwise

Warren, yes, or....

... Figure of 8 !

it could go even more Logan's Run and feature only 1970s era Jenny Agutter lookalikes wearing just shimmering silky togas.

Excuse me a minute...