Welsh for Spanish?
It would be interesting to find out if there was significant demand for such a course, given the significant Welsh-speaking community in Patagonia, and perhaps the US Hispanic members of Duolingo might also attempt such a course. Certainly, the reverse course would be viable in Wales!
I would like to learn spanish from Welsh and as rmcode says it would be a useful resource for schools in Wales - Welsh or English medium. Even if english is your first language, I have heard that daisychaining languages is recommended by a lot of people who seem to have the knack of learning lots of languages.