Anybody with high round count 17s?  What's the expected barrel life on these three things?  And when it does get shot out, how easy is it going to be to get it rebarelled?

~30,000 rounds. The barrel is changed by loosening six screws, removing the barrel assembly, sliding the new barrel assembly in, and tightening the six bolts with an in/lb torque wrench.

It's easy to rebarrel, cost roughly $1,100 for a new barrel assembly. You'll shoot well over 30k rounds before you notice diminishing accuracy as long as you're not puposely trying to burn it out.

Are barrel assemblies readily available?  Where can you get one?

Midwest Gun Works has them from time to time.

Hi Desert Dog has them in stock a good bit of the time.

SCAR Barrels

I think you could also contact FN to get them.

You will go broke before you shoot out the barrel.  1.  It is CHF barrel  2. CL bore  3.  308 is not going to wear the barrel as fast as 5.56 because it produces less heat and friction since it is a slower projectile
30K sounds reasonable from what others have said .... You could probably still get more after 30K but I bet you will need a new bolt before you need a new barrel.
Barrel changes are easy on the SCAR tons of youtube videos that outline and show you how to do it.