You don't need a special TV for MHL, you just need an adapter dongle, just like with SlimPort. "MHL-enabled" TVs and monitors just do away with the need for a dongle, so that you can use a direct micro USB to HDMI cable instead. IMO, the dongle is a more practical solution, without the need for proprietary cables.
Also, MHL (both adapters and built-in solutions) charge the phone while it's used.
Adding a second port is neither necessary or practical in a mobile device. They just need to make sure the USB port can handle both MHL and USB OTG at the same time, and then add an USB port on the dongle, or a hub in the TV/monitor. Simple, cheap, effective; uses current, not future, technology.
And, falling prices on everything but flagship mobiles? Have high-end laptops or PC components dropped in price recently? No, if anything, they've gone up, as ever more "premium" features are added. The same goes for phones. Flagships use cutting edge components, which carry a significant premium. I'm not saying that either necessary or fair, but it's the way the world works as of now. Then again, midrange phones are now "good enough" for most uses - which they truly weren't just one or two years ago - so today you can get a great phone for very little money. Just look at the Moto G or Zenfone 2.