Finally got a PCB made for a USB JTAG adapter using FT2232 chip. This has been on the todo list for some years now.
This is a lite version without additional buffers so it should work with target voltages from about 2.8V to 5V. There is also a second PCB version with buffers that should be capable of supporting target voltages from 1.65V to 5V.
JTAG interface like this can be used with OpenOCD for example.