1) Your question is about FUTURE processors for that socket. It's my understanding there WILL be better models coming for FM2+, both CPU's and APU's.
It's AM3+ that is definitely dead for future processors.
2) R9-280?
It's not that much better than an R9-270X, and while I'd like to recommend it the price you mention indicates the cheapest card. Since I can't find any reviews yet I'm pretty nervous about what the quality will be.
The Gigabyte R9-270X on the other hand is just under $200 (comes with two free game codes for choice among Silver tier so make sure to get that sorted):
http://pcpartpicker.com/part/gigabyte-video-card-gvr927xoc2gd
I suspect the Gigabyte R9-270X would be a higher quality card, and probably perform the same as the R9-280 possibly even higher as I'm guessing the GPU frequency would be a bit lower due to saving money on the cooler. I saw an XFX R9-280 at around 850Mhz, and I think the Gigabyte R9-270X is 1000Mhz for the cheaper model but I forget. (The R9-280 is maybe 5% to 8% faster if the clocks are the same)
3) BOTTLENECK?
On average, the R9-270X/280 would not be a bottleneck. It does vary by the game however, and there are a few very demanding games that would bottleneck. METRO Last Light is one of them.