Spain operates like an asymmetric confederacy in key areas – some regions manage their own taxes, security, as well as schooling and public media – although it maintains that it’s a state of autonomies.
I doubt this will be reversed, even if governments halt further devolution. There isn’t the political capital – or narrative – to recentralise power.
Growing regionalism is especially a threat to Spain’s national story. The inequality of treatment and privileges between supposed equals can destroy the narrative of Spain as one people, one state.
This doesn’t necessarily mean that Spain will devolve into micro-states, but it’s a reminder that de facto > de jure. Brexit, the Catalan declaration of independence in 2017, and UN resolutions are all WEAK politics attempting to play _de jure_. Navarre’s gradual devolution – see log/25/, Catalonia’s collection of income tax, and Norway and Switzerland’s relationship with the EU are STRONG politics that care about _de facto_ reality.