Best 36er to "accessorize."

Yeah, the Coker is a great deal at the current price: lightweight and stiff frame, plenty tough for off-road (see what BrianO is doing with his).

As far as upgrades, if you really want ISIS down the road you can swap in a Nimbus 48h ISIS hub and KH frame (UDC was recently selling KH36 frames for $100 but we probably won’t see those prices again). If you’re concerned about the weight of 48 spokes you could re-lace using 24 spokes. Though IMO until you do something about the tube (29er or Foss tube) and tire, the extra spoke weight isn’t worth worrying about. The main limitation with this route is that moving to a Schlumpf hub would also require a new 36h rim (though it seems that most people going geared opt to buy an entire wheel anyway so as to have a backup).