Systems like the SA-10 are already proliferating around the world. For open source, try -
http://en.wikipedia.org/wiki/S-300_(missile) - and scroll down to see which countries have them, or are thought to be trying to get them. It includes old favourites such as Iran, Syria, Serbia, and Libya amongst others. When a system is as mobile as the SA-10 a country doesn't have to have very many at all before lots of pilots of 4th Gen airplanes are going to have trouble clearing their ears on the first night of the next Op. And it can be pretty hard (and expensive) to target them with cruise missiles if the SAM operator knows what he's doing.
To go back to LowObservable's earlier points:
Venlet, as the PEO, is required to ensure LM deliver an ORD-compliant Block 3 aircraft on budget. TBR was an excellent exercise for him to open all the cupboards, air all the skeletons and blame anything and everything on his predecessors. You can rest assured that he is staking his career on the price and timeline in the results of the TBR so in his mind it's as accurate as it can possibly be. But he doesn't tell the Services or Partners when they can or can't declare IOC. The USAF have squadrons of F-22s, Block 50 F-16s, Rivet Joints, JSTARS etc and are prepared to wait until Block 3 is full-up until they declare IOC. The USMC with their tired fleets of AV-8Bs and legacy F-18s have a much greater degree of urgency and, after careful analysis of the Block 2B capabilities, are content that it is enough to be going on with. The UK can make their own choice on what constitutes IOC. A Block 2B F-35 will have more air-ground capability than one RAF aircraft currently on Ops over Libya has right now.
It may be arrogant to say that there is no alternative. Or it may just be true. So what is the alternative you're proposing? Trying to reverse engineer stealth characteristics into existing platforms? I'm no LO design expert, but in my very limited knowledge you need things like aligned edges, an absolute minimum of very carefully designed protuberances - scoops, holes, air data probes, aerials, fuel dump pipes etc, a carefully designed sub-structure, bendy intakes to conceal your engine face, some magic around the back end to hide your jetpipe, an embedded targeting pod built into the airframe, an AESA radar if you don't have one already and the application of easily maintainable coatings + many more. There's a fair bit more to it than putting on some conformal fuel tanks and bolting on a stealthy weapons pod. By the time you've spent all the money to do that, wouldn't you just prefer to have a purpose-built, brand new airplane that's at the beginning of its growth cycle? (and in the UK's case, to be a Level 1 partner in the manufacture of lots and lots of those new airplanes so they almost come for free)
And finally, before I go down the pub for the night, it's well known that there are fighter missions that don't require stealth. F-35 was explicitly designed for them too. When you've cleaned out all the nasty threats, you bolt on the 6 external pylons and the gun, add some double ejector racks and play to your heart's content, in an airplane that gives you more SA than you've ever dreamed was possible - an APG-81, EOTS, DAS, L16 etc and all shared at very high data rates over MADL with all your coalition buddies in their F-35s too.
Regards,
Single Seat, Single Engine, The Only Way To Fly!