It's hard to give a accurate answer on that right now. That's something which would be decided at the time. But my guesses are this would be possible in the feature.
Please take note that even this position is voluntarily, we do expect commitment when applying. So one should not expect to get into a future Spanish server by joining the English server. One should apply to the English server because he/she wants to serve the community as a Moderator.
Opportunities might arise in the future, but nothing has been set in stone.