Beyond merely the frequencies themselves, there's a ton of logistics involved in things like harmonic or other interference and propagation, all of this related to power. However, it is increasingly such that a lot of devices are software-based radios, so changes to a lot of existing technology could be just a firmware upgrade, if possible.
Unfortunately, we are not yet at the point where a range of frequencies anywhere near as wide as discussed in the article can be supported by a simple firmware upgrade. RF receivers typically include a very narrow bandpass filter as the first component after the antenna. As spectrum becomes more crowded, these filters are even more critical to prevent saturation of the low-noise amplifier and unwanted products from the downconverter/mixer.
In my experience, the ADC is far from the limiting factor for linearity in an SDR receiver. The analog components up front (LNA and mixer, especially) are the limiting components. Broadband front ends make it even worse, because it's more likely you'll have an interferer passed through the filtering, even if it's nowhere near (in frequency) your signal.
Don't forget the antenna. In many cases, the antennas themselves have specific polarization and beamwidth/radiation patterns along with SWR that is directly tied to the frequency range of the antenna itself. SDR doesn't change any of this.
