Mark-up languages will die. They're fine for marking up text with styles and links. That's all they're good for. Highly inefficient waste of network resources. All these cobblings atop of HTTP, especially ones based on XML are a joke.
Performance problems add up.
There is no reason that today's software, doing as little as it actually does, has to be so bloated. BeOS is a perfect example of what good design can gain you, from the size and speed angles. XML 1.0 has entities. Sure, entities will die. As usual, I should say that the rare letters from Mr. Clark are worth hundreds of 'ordinary' letters in XML maling lists.