I think the past 60 years of engine development have proven that single engines are not as much a liability as first thought of in the '50s. There used to be regulations stating that no 2-engine airlines can be operated over water, as well. That was changed as the technology and the power of those engines continued to improve. Now the Boeing 777 can operate safely with 1 engine running, even!
The thing is the Navy doesn't need an Air Superiority fighter. It's not replacing an Air Superiority fighter. The Hornet and Super Hornet are NOT air superiority fighters. They're attack craft that can defend themselves when they go in to bomb ground targets. The Navy hasn't had Air Superiority fighters in a long long time.
That's not what it's replacing, and that's not what it should be.
Engine development, greater thrust, greater efficiency, greater reliability are all great but thrust still = 0 when one engine goes out. Also, someone actually believes Pratt & Whitney that it'll never fail? Grumman advertised the F-14 as being "unspinnable." It didn't work out that way and believing in P&W's "never" failing engine won't either. Also, don't forget that an engine failure can occur for numerous reasons, not all of them internal to the engine that will "never" fail. Those advocating for the single engine have probably never been by themselves, out of radio contact, 500 miles away from the CV and 2,000 miles away from land and gotten an oil-pressure light or rising EGT or busted bleed duct or nozzle failure or engine boost pump failure or any of the other myriad things that can go wrong with hi-tech machinery. How about the possibility of a simple fastener that was stripped by the 18-year-old plane captain that works its way loose and down your intake? Something that small can cause a small chip in a fan blade that causes two chips in the 1st stage compressor which leads eventually to a catastrophic engine failure as it eats itself up. Who doesn't fly fighters in that environment? The US Air Force. Any guesses who struck out "twin" and penciled in "single" in the statement of work? The single engine decision is probably the biggest single (no pun intended) real "cost" of a single airframe for three services. Also, who the heck else is building a single-engined fourth or fifth generation fighter? NOBODY...but us. The Rafale, Typhoon, F-22, SU-27, SU-3x, MiG-29, are all twins as are both the Russian T-50 and Chinese J-20. Off the top of my head I think the F-16, Mirage 2000, and J-10 are the only single engine aircraft that would be considered anyone's front line fighter and the only "new" one of those three is the J-10 (which is just a Chinese knockoff of the Israeli knockoff of the F-16).
As for the air superiority thing, well, you're just wrong Krusty. In any realistic evaluation the primary mission for all the Hornets remains air-to-mud but it's not because of the airframe or because air superiority isn't a Naval Aviation mission, it is. In my experience, some of the lack of emphasis comes from the historical development of the community. The original Hornet drivers came from the A-7 community and thought that all they needed to proclaim themselves "fighter pilots" (besides going USAF where they think everything is a "fighter") was a pointy nose and twin tails but they still flew like attack pukes. They were so cute...like kittens with all their snarling and little claws and constant sucking at the tanker tit. The Tomcats, being the grown up cats, would just bat them away and they'd run off and go drop green turds on the ground somewhere. They were good at dropping stuff but sucked in the air even with all their brand new geewizz computers helping them fly their planes. It's gotten better over the years primarily because of the Tomcat squadron transitions but most of their training $$$ still goes to air-to-ground. That's driven by the real-world fact that we've been fighting since 1990 against enemies with little to no air-to-air capability but there are plenty of countries that do and that number is growing so air superiority will continue to be a requirement.
Now, philosophy and doctrine aside, is the Hornet/Super Hornet an "air superiority fighter" or not? Of course it is. Download the bomb crap and upload AMRAAMs and AIM-9X and all variants can take on anything currently out there. In particular, the Super Hornet with AESA radar is pretty amazing. It can't turn quite as well as some fighters but what people don't understand is that in an air-to-air missile environment this supermaneuvability and post-stall maneuvering is mostly a bunch of crap. Let some SU-27 drop anchor to try his "Cobra" and I'd have an AIM-9X up his prettythang in two seconds and be on my way. Why have the airplane do all that turning when the missile can do it better? Supermaneuverability is sexy and sells airplanes but I don't see that much tactical utility in it.
The thing that really slays me about the F-35 though is the cost of the plane. In the 1990's the Navy decided to buy the Super Hornet over the advanced Tomcat because, they claimed, of the Tomcat's extraordinarily high $50M per unit cost. So, how much does the F-18E/F cost? Oh, round $55M. Now they're buying an airplane that is supposed to run...wait for it....$115M-$135M. That's what some program guys are claiming but program guys have never, ever, been an accurate source, you can tell they're lying because their lips are moving. For instance, they like to leave out little things like Government Furnished Equipment (GFE) where the government procures things like Inertial Navigation Systems, Electronic Warfare Systems, or Ejection Seats on different contracts and then furnishes them to the airframe builder to install. Actual costs based on experience with the F-22 production shows we're looking at closer to $200M per copy, the same as an F-22. Why so expensive? Probably a lot of it is because of all of the still changing requirements from all of the different customers and changing procurement numbers. It's a vicious circle where lower numbers procured means higher cost per unit and the higher cost per unit leads to lower procurement numbers and so on. The rest is unanticipated delays based on unrealistic expectations prior to development and production problems. A million here, a million there eventually adds up to real money.
The idiotic claims by the press about the F-35 burning holes in carrier decks aside, there's a real problem here and what choices do we have? F-15's, F-16's and legacy F-18's are falling apart and with Obama's half-a-trillion dollar cut to defense beginning next year we won't be able to maintain but a few of these platforms so what are we going to do besides bitting the bullet and getting the F-35 deployed?