It will be interesting to compare the effect on Camino numbers of the eclipse in 2026 with the Holy Year effect. Looking at the path of totality, it seems to cover most of the Frances, the Norte, the Primitivo, the Ingles, and a number of smaller routes. I can certainly imagine there will be a number of people shifting their Camino to coincide with the eclipse, who might not otherwise choose to walk in August. I expect that there we will see both some increase in numbers as well as a shift within the year making August busier but some other parts of the year less busy. On the other hand, I don't expect that little villages in the meseta will fill up. There is just too much of Spain in totality and too many places with more to attract normal folk and easier to get to than our little villages.
If you miss the 2026 total eclipse, there is another just a year later, in early August 2027 in Spain again. But this one is at the very southern tip of Spain. Not so close to many popular Caminos and not the time I'd want to walk there.