I remember the announcement that they were "going to" implement that system, and had wondered whether it ever really happened. Since typically no new system is put in place at any AoT airport without a dozen press releases, speeches, demonstrations, and announcements that the event makes Thailand the best in the world, however, and given that there has been no such circus, I'm inclined to think that the system hasn't been implemented.
Inline baggage x-ray systems do exist, and are largely automated. At Incheon in Korea, I've had my bag come out with a little device bolted to the handle and playing music. When you go past the customs officer with that device, you're sent to a nearby station where another officer looks at the number on the device and pulls up the x-ray image that triggered the inquiry. (In my case, it was a few bottles of wine which I was permitted to bring in, so the guy simply removed the music box and sent me on my way.)
So yes, it's not unrealistic to believe that BKK could also install and operate a similar system - though whether they've actually done so is still unclear.