Originally Posted by grolby

1. Yep, the Rohloff has enough gears. Actually, the Nexus-8 and new SRAM 9-speed hub might have enough, too, depending upon how many you feel you need.
2. Don't forget the front derailer and two extra chainrings, plus the chain links that you get to delete.
3. Hubs can already take this kind of treatment better than a derailer can. There are some concerns as to whether the Nexus can survive big hits, but I suspect that it's probably pretty tough. This is a non-issue for the Rohloff, which is damn near impossible to break, and the new SRAM hub is supposed to be pretty tough as well.
4. This is simply asking too much. The design of an internal gear hub cannot allow it to meet both of these requirements at once. It may be possible to design a hub and corresponding dropouts that will allow the use of a quick-release of some kind, but I can tell you that this almost certainly won't happen with normal vertical dropouts.
5. There are multiple hubs on the market with these capabilities.

You have some stringent requirements - an internal hub must be lighter AND tougher AND more reliable AND fully interchangeable with derailer wheels. You give the impression that unless an internal gear hub meets every one of these requirements, that it cannot be superior to derailers. That doesn't make much sense to me. Making a decision about your drivetrain or other tech on your bike must always involve certain trade-offs. In certain areas, modern hubs are so far ahead of derailers that it's not even funny (reliable shifting in any conditions you can think of is one of them). In others, derailers still have an edge. If internal-gear hubs were to meet all of these requirements, there would be no more reason to have derailers installed on ANY bike. It would make a lot more sense to make a list of your needs and then see which system fits them better, rather than simply saying "if it isn't better in every way, I'm not buying in."

The sliding dropouts look sweet. I must admit that the presence of moving parts and smaller tiddly bits would make me a bit nervous, but if the engineering is sound then it's an elegant solution to the horizontal dropout problem. It would be pretty neat to see a simple standard design adopted, and installed on most frames, that would allow the use of whatever drivetrain you wanted. Perhaps someday...