Sorry, but you're not being realistic about this. The reasons are endless.
The "backlash" you're talking about would come from a tiny fraction of the user base. The people who blather on these forums all daylike me and youare not representative of the user population. Over 90% of computer users make purchases without looking at benchmarks. (Source: multiple studies of consumer purchasing decisions I ran in my last career in market research.)
Actually, what you proposed would cost Apple more. As I stated above, an Iris 5200 + a dGPU would be cost prohibitive. The 2.4Ghz + 5200 combo costs a whopping $657. And keep in mind that's far away from Haswell's top speed.
iGPUs are the future for Apple laptops. There's a reason Intel's been throwing ridiculous sums of money into developing this stuff. An integrated platform offers tremendous power savings potential, not to mention better profit and revenue for Intel.
Apple has not chosen to prioritize graphics power in their laptops. Every generation, you'll find other cards they could have chosen, but didn't for reasons of power consumption. Apple's priority is marketing size, form, and function (i.e., slim and long battery life) above power.
Note that you won't even find the words "NVIDIA" or "650M" in the text on Apple's current MacBook Pro web page on performancethe very page that specifically talks about graphics. You have to go all the way down to the tiny footnotes.
We return to marketing, and lo and behold, there are numerous benchmarks where the Iris 5200 beats the 650M. Cherry-picked, sure, but in marketing, that doesn't matter. Being able to show even one pretty bar graph while touting increased batter life is incredibly powerful for marketing.
Seriously, I'd love a dGPU too, but it's not going to happen.
You make good points, but your pricing is not entirely correct. Apple would not use the $657 part as a default, it would be a BTO option and you'd pay the premium for it. The 2.4 Ghz part I quoted was for a 28W i5 with HD5100.
Also, I agree that consumers and people who buy iToys do not care about specs but the Pro users definitely do. Especially on a $2500+ laptop.
I am just making guesses, that is all. But as far as $ is concerened, I think it can be done. Time will tell