What is the origin of rotational energy barrier in ethane?
As you say, this issue appears to be unsettled. I find the argument in favor of hyperconjugation compelling, but there is theoretical evidence that steric strain contributes as well.
This debate is about 20 years old. Here are two papers summarizing the opposing views:

Pophristic, V.; Goodman, L. (2001). &quot;Hyperconjugation not steric repulsion leads to the staggered structure of ethane&quot;. Nature. 411 (6837): 565–8. doi:10.1038/35079036.
Bickelhaupt, F.M.; Baerends (2003). &quot;The case for steric repulsion causing the staggered conformation of ethane&quot;. Angew. Chem. Int. Ed. 42 (35): 4183–4188. doi:10.1002/anie.200350947.

A more recent paper that has an interesting take:

Baranac-Stojanović, M. (2015). &quot;Theoretical analysis of the rotational barrier in ethane: cause and consequences&quot;. Structural Chemistry. 26 (4): 989–996. doi:10.1007/s11224-014-0557-5.

I cannot read the entire article, but the abstract offers the conclusion that hyperconjugation is responsible for the initial energy rise during rotation, but that steric factors are needed to fully explain the high energy of the eclipsed conformation.