Swatches would be useful, but producing them is not a straightforward business.
Most of the companies which sell a wide range of fountain pen ink have made an attempt, some more successfully than others:
Goulet Pens in particular have put a lot of effort into it. The comparison tool is a real boon to customers, because every single swatch is on the same paper and photographed with the same lighting and white balance - so if the colours are a bit off, at least they're all off in the same way. If anyone wants swatches of fountain pen ink, that's as good a place to go as any.
It would be a different proposition for a disparate group of calligraphers to attempt the same. For colour comparisons to be meaningful a standard light source would have to be agreed, and although daylight sounds great it does vary a good deal. White balance would have to be set manually, which is more of an art than a science, and a standard, widely available paper would be essential. I don't want to put people off, but these are significant problems.
On the other hand, notes on flow, line quality and so forth would be well worth having.