Bluetooth is a wonderful thing, however, a lot of stuff doesnt support it. Things which do are often, due to the costs of development and the end product, only the most saleable items, such as full sized QWERTY keyboards or mice.
Usually when these devices set up a Bluetooth connection to the host
they'd invoke the appropriate service, sending data that conforms to this protocol. This has its limitations in that one can't simply use any device to communicate with the host: it must be supported by a Bluetooth service, or by a custom one.
As most devices have USB connections the solution to this could be to simply broadcast the USB signals, which could then be accepted by the computer and run through port emulation software, so that the device appears as if it were connected to an ordinary USB port. The standard Bluetooth serial connection service may be used for this, although it might be more efficient and reliable to use a custom one.
As many devices can be run from the same USB receiver, it would be possible to emulate more than one USB port, or even have more than one socket in a transmitter (although this would still tie peripherals together, it may be useful for systems that use barcode scanners or other obscure hardware). The transmitter itself would have to be rechargeable, as it would have to power itself and supply the usual USB +5v power to its connected peripherals. It may be possible to formulate a design which allows one to clip it onto a peripheral, eliminating the trailing wire altogether.
Although I am aware these already exist for printers, they won't work for any other device, as they don't send the raw signals. As with the Bluetooth printer connections, price would be a serious limiting factor, as the transmitter would have to be relatively intelligent, however, Bluetooth device costs are constantly plummeting, and there are some systems where this may be a requirement, for example where wiring cannot be easily run from the system to its peripherals. The fact that the device doesn't have to understand a protocol (as with the printer links) would also reduce the final cost.