1) How big is his camera's native color space? No point having anything bigger than this
2) How big is his fine art paper/printer combo color space? No point having anything bigger than this.
Couple points to address both 1 & 2. Digital cameras don't really have a color gamut (they do have a color mixing function). There is some assumed internal color space a converter has to start with and only the manufacturer would really know this although with the right equipment one could end up with the spectral sensitivities and get very close. Then there's the internal color space of the converter to process our data.
Building an ICC profile doesn't tell us all that much since the target has a gamut. The data feed to the profiler is output referred (processed).
The scene has a gamut. Point the same capture device at a gray card and a sunlit scene of colorful flowers, you end up with different results.
Bottom line using say an Adobe raw converter is that at some point, we're dealing with ProPhoto RGB primaries and thus a gamut. If you work with Adobe RGB (1998), you will clip colors from some (how many?) captures. I think that's illustrated in the video. It's easy to examine this in ACR too. IF your goal is to render all the possible color, you don't want to select Adobe RGB (1998). IF your goal is to see all the colors on-screen, get a wide gamut display and encode in Adobe RGB (1998).
There's a big disconnect in the shape of RGB working spaces and output spaces so keep that in mind. There are vastly wider gamut that can be defined in something like ProPhoto RGB than you could possibly output, true. But we have to live with a disconnect between the simple shapes of RGB working space and the more complex shapes of output color spaces to the point we're trying to fit round pegs in square holes. To do this, you need a much larger square hole. Simple matrix profiles of RGB working spaces when plotted 3 dimensionally illustrate that they reach their maximum saturation at high luminance levels. The opposite is seen with print (output) color spaces. Printers produce color by adding ink or some colorant, working space profiles are based on building more saturation by adding more light due to the differences in subtractive and additive color models. To counter this, you need a really big RGB working space like ProPhoto RGB, again due to the simple size and to fit the round peg in the bigger square hole. Their shapes are simple and predictable. Then there is the issue of very dark colors of intense saturation which do occur in nature and we can capture with many devices. Many of these colors fall outside Adobe RGB (1998) and when you encode into such a space, you clip the colors to the degree that smooth gradations become solid blobs in print, again due to the dissimilar shapes and differences in how the two spaces relate to luminance.
The gamut of the output device you aim for today, and what you might aim for tomorrow is unknown. So again, why encode in a working space that limits this?