After working at a company using SDRs, I realized that a well performing SDR is a lot more than an antenna, a DAC/ADC, amplifiers and a processor. You still have analog paths you need to worry about and for many applications those aren't going to cover your 1GHz range. You need to worry about noise, amplification, signal fidelity, etc. You still need a good portion of what makes up a traditional radio. Sure, there are narrowband, low power SDR xcvrs and xmitters but that's not the same thing.

That said, a long time ago I made a test fixture for a 6-bit, 12GHz DAC and it was cool to run it as an arbitrary waveform generator.