All of these different ports you don't want serve a specific purpose. Designing a universal electrical interface and connector that satisfy every purpose would be difficult to impossible, not to mention that having separate interfaces for separate purposes reduces confusion. I'll agree it could be potentially awesome, though. Each design in use has tradeoffs between latency, throughput, distance, resilience to interference, etc.
Ethernet is designed for low-ish latency, moderate bandwidth, and long distances. It does not have enough bandwidth to replace HDMI, and Ethernet routing and addressing is not well-suited to the problems solved by USB. My own testing has shown that 802.11g will not often exceed ~15mbit/s, even with a device sitting right next to the access point. All devices on a wireless network have to share the same 54mbit/s with each other and with any other noise that happens to interfere. Switched Ethernet gives the full bandwidth to all devices, all the time.
HDMI and DVI are designed for direct, zero-latency, high-bandwidth links over medium distances. The current iteration of HDMI specifies a bit rate of 10.2 gigabits per second, over distances up to ~50 feet. It's a one-way interface (for now). Since it's mostly unidirectional, and doesn't have any kind of routing, it could not replace USB. If you added USB-like bus features, it would likely not be fast enough for displays.
USB is designed with a simple master/slave hierarchical bus topology, which is ideal for desktop peripherals. Even USB3 at 5gbit/s isn't enough to replace HDMI, and that 5gbit/s is used for control as well as data, and shared across all devices on a particular interface. Plus, USB cannot exceed 15 feet without repeaters.
USB is also not well-suited to replace PCI(e) for graphics adapters, because PCI(e) allows for very-low-latency communication, DMA, etc.