WHY WOULD WE ABANDON OUR CAPITAL?
Lurker's comment:
I believe it's not that uncommon for a conquest game. Lanzelot can best answer why he likes the idea - I think he still does - but I would guess it has a lot to do with your current landmass being so small and insular.
If you conquer the Dutch - that would be a prerequisite for moving the capital anyway - you will perhaps see a better spot for a capital with more space around it and a shorter supply line to your new front.
Your current core will always remain very limited, no space for a second ring will mean only few towns will have low corruption. There's not much that a capital can do in such a small space.
If you're moving, you would first build an FP next to Berlin, this will be quick to build and also help with corruption in your old core when Berlin is gone.
If you're abandoning Berlin you don't need a MGL to rush a new palace somewhere, a palace will automatically get asigned to another town. There is a ruleset by which the game decides what is going to be the new palace and I'm sure the size of the population has a lot to do with it, but hopefully somebody knows the rule better than I do.
If you build your new palace instead of auto-moving it you will spend a lot of shields. There is also the problem that in the current location Berlin will start to compete for tiles with the towns surrounding it. As you haven't invested in Berlin apart from a 20-shield barracks, you stand little to lose when abandoning it.
There's probably stuff you can throw against a palace move in this game. I'm not familiar with this type of game, so I'll leave the discussion to the experts.