Some of you might know that It has already been tried here under the guise of "Top's club" trialled in Central Rama 2 over a year ago.
The business model was based heavily on the Costco model, and indeed many of the products were Kirkland branded products. Layout was the same, staff uniforms were the same, but product range weighed more towards food rather than non food items. However the non food items were typical Costco other than electrical.
The investment appears to have been enormous, and I suspect there was some tie up with Costco, but the prices were not as attractive as they should have been [maybe import duty?]
It was tried for over a year, but did not attract the level of customers it should have done, and it was closed after a one year trial.
My wife and I both miss it, as it was the closest to the "Costco experience" you get in Thailand.,,,brave try though, and well done to the Central Group.