I installed PhotoshopCC Trial to test new features of ACR 8.1 And it was very pleasant surprise, that 2000 files limit gone.
Just because you cando something doesn't mean you should...Camera Raw was designed to be able to open multiple raw files at once, yes...but not opening thousands of files at once. Camera Raw is a plug-in that has to get it's ram allocated by Photoshop. As such, trying to open that many files is going to severely tax both Camera Raw and Photoshop. You wouldn't open thousands of images into Photoshop at once would you?
You would be far better off if you simply selected the images in Bridge and used Image Processor to save out the images.
I used CS4, CS5, CS6 and now use CC. CS5 was able to load CPU at 98% at saving process. Bridge is something strange - I couldnt find no 1 reason to use it. ACR for me - analog of "black room" where I could fix exponometr errors, crop image remove red eye and similar. And ACR is very good - and much more user friendly than more cheaper Lightroom. I dindt want make collections or other staff - I able copy or move fotos to folders with file manager.
But ACR6 and ACR7 was limited - they could open only 2000 RAW files. On vacation I got 13000 - so in CS6 I opened it partially - and then CC was realised. And occasionly I opened 2500 files and there was not errors - they opened. And I was really happy - because I often need to workout more than 2000 files at once - and made in one time is much more simpler. But - why Photoshop lost its ability to use all system power - I couldnt understand. And Im sure - if ACR will use 100% of my PC power - 1 foto will be saved at less then 1 sec. If Adobe thinks that option of saving fotos in background is needed for most part of users - let they give for rest option to save it in foreground - like was in CS5.
Have you created a very large ACR disk cache, in ACR preferences? Don't know that it will help, but it's the first thing I would check.
ACR can be hosted indistinctly by Photoshop or by Bridge.
With the sheer numbers of images you want to open simultaneously, you would be foolish not to give Bridge a try. As I said, you can use Bridge from Bridge too, even have Bridge host ACR with all its functionality without even having to run Photoshop—although of course you can run Bridge and Photoshop at the same time.
Bridge started out as nothing more and nothing less than the old Photoshop File Browser, and it remains exactly that.