They sound dead serious

That is a terrible pun, and you should be burned.

Honestly, I've currently got Biel-Tan tagged, but will absolutely go Saim-Hann if they actually give us a way to be Saim-Hann as opposed to, y'know, Biel-Tan Red Edition.

Saim-Hann with vehicle bonuses? Idk. Lowered vehicle requisition cost?

perhaps a special hero class/class--saim hann wild rider/wild rider chieftan? *shrug*

Maybe something really different. Lowered vehicle cost sounds so boring trait. Not gonna speculate here, but if subfaction differences aren't really interesting/diverse then devs have failed on that sector.

Too many games these days have so dull racial/faction traits.

But let's hope for the best!

E: But not dismissing lower vehicles cost. It could be one of the traits among the rest. But as a lonely saim-hann bonus dull.

Also a good thing to remember is that if, say, Saim-Hann Jetbikes (Wild Riders) would be a cheaper version of other Eldar Jetbikes (or had some other benefit), why would anyone ever use a jetbike if their subfaction wasn't Saim-Hann?

That is an important thing to consider when creating subfaction-abilities. Got to remember to keep all the other subfactions viable with their benefits as well.

True, but it comes down to what you prefer to play. If you realllly want to ride jetbikes all the time, then you will go Saim-Hann. Otherwise you will go something else.