Second, there's all the log-aesthetic stuff from Japan, [2] has links to a lot of papers. Honestly, I find their claims of aesthetic beauty to be fluffy, not backed up by hard empirical evidence. I did do a small amount of human evaluation research in [3], which suggests that the log-aesthetic curves are visually pleasing, but the math for their use in an interpolating spline (which is the subject of TFA) is less stable than Hobby splines, Euler spiral splines, or Minimum Energy Curves (all of which are fairly similar).
I think there's more that could be done here. Thanks for your question.
[1]: Fred Attneave. Some informational aspects of visual perception. Psychological Review, 61(3):183–193, 1954.
[2]: https://www.yoshida-lab.net/english/research-e/log-aesthetic...
The OP talks about aesthetic curves, but most comments are about continuity and smoothness. Intuitively that makes sense. Do you happen to know if there is any serious research that looked into which 2D curve properties do people find aesthetically pleasing?