I proxied a Mekanized Ork army yesterday after hearing nay-sayers talk down the kans.
IMO, the trick with kans is to just max out vehicles.
We did a 2500 point single force org game.
I took:
2 Big Meks, kustom force fields, 2x oil grots, each mounted in a Mekboy Junka (AV11/11/10) armied with 3x twin-rokkits and supa zzaap gun, and reinforced ram.
3x3 Nobs, all with shoota/skorchas, mounted in battle wagons with killkannons and dethrollas.
4x Trukk Boyz with rokkit, mounted in trukk with rokkit
3x3 Buggies, twin-linked rokkits
3x3 Killa Kans, big shootas
Armor Break Down:
3x AV14/12/10
2x
AV 12/12/10
11x AV11/11/10
13x AV10/10/10
29 Vehicles!
The Dark Eldar simply couldn't keep pace on popping vehicles. Kans made it through the game by posting up behind vehicle wreckage for cover and blasting away with the big shootas. Big Meks got targeted early, and they really aren't that effective (but do draw off a lot of fire).
By the end of the game, the table looked like this:
http://digitaljournalist.org/issue0212/pt04.html
Was a ton of fun to play, and play against.
I like the idea of converting up a ton of vehicles, so this type of army is now in line at my modeling desk.
-Matt