AMD will not be making separate AM3/AM3+ Bulldozer's. There will be only AM3+ versions, and should motherboard manufacturer's somehow get them running in AM3 boards, good for them, but it will be unsupported by AMD.
As for mid-range and lower processors, I highly doubt the AM3+ platform will see anything other than AMD FX series processors. I suspect that like lga1366, AM3+ will be exclusively high-end, and that all mid-range will be powered by the Llano A-series APUs, and the low-end/ULV powered by the Brazos C/E-series APUs. Could that change? Sure. But if it does, any slower AM3+ chips will certainly not get the FX moniker.
Here's a list of the upcoming mid-range products.