This could be an interesting concept, as Spain has both quite unique terrain and scenery, along with el pato (if you know your trains you’ll know what I mean) and gauge changing trains. There aren’t many Western European routes that aren’t in the uk currently (maybe Germany is an exception), so why not change that? A route like Madrid - Alicante could be interesting, as it just recently got AVE high speed services in 2017. If you lot have any other opinions? Let me know!
Also forgot to mention ‘los patitos’ as well (again, you’ll know what I mean if you know the Spanish high speed network)