I don't really see any evidence for substantial spending on antibiotic R&D. If you can point to some kind of citation for this I'm certainly curious.
Antibiotics aren't really a chemical class either, since there are many mechanisms of action. A chemical class would be something like beta-lactam antibiotics, etc. I suspect that particular class is mostly played-out, but there are potentially as many mechanisms for attacking bacteria as there are unique metabolic pathways in bacteria.
I don't mean to trivialize drug development - it seems to have slowed down across the board which probably reflects that most of the "low-hanging fruit" is gone. I think it is a far stretch to go from that to saying that there won't be any new drugs of any particular kind.
Looking at this, it seems like we have about 75k MRSA cases per year. If you want to make a decent profit of around $100M/yr off of that, then you need to charge about $1500 per case. That wouldn't be an amazing blockbuster, but it probably would be sustainable. If you could charge $15k/case then it would be a solidly profitable drug.
There are a few problems with those numbers. One is whether introducing an antibiotic would reduce the incidence rate. Obviously we would want it to, but that means fewer cases, and so you need to charge more per case. Also, what percentage of those cases are among people with insurance willing to pay those kinds of fees for treatment. If you end up treating people for a reduced charge or for free, then again there isn't much profit.
If some first world nation offered a bounty for a treatment that made up for these shortcomings I bet you'd see a determined effort to discover a new antibiotic.