Coastal defenses that are powerful enough to stop capital ships were extremely rare, because they were prohibitively expensive. In game terms, this would be like max level bunkers/fortifications, RRG's, and AA batteries all along the coast, with fully developed infrastructure to mimic good communication channels and resupply/reinforcement corridors. You are free to build that, if you want. It will cost you quite a bit, but it's a bit quicker than building a navy, because there's less research involved.
But, I really don't want to see more types of structures, especially defensive ones. Noobs and AI countries already waste all their resources building that junk. It doesn't stop anyone because you just go around them, and they don't know how to build stacks effective in attack OR defense. More structures would just make the game slower, and less challenging at the same time. Get rid of propaganda and defensive structures, if you want to help even out the game and make it more fun. Every penny NOT wasted on structures could go into units, produce more action, and make wins more challenging.
But, I really don't want to see more types of structures, especially defensive ones. Noobs and AI countries already waste all their resources building that junk. It doesn't stop anyone because you just go around them, and they don't know how to build stacks effective in attack OR defense. More structures would just make the game slower, and less challenging at the same time. Get rid of propaganda and defensive structures, if you want to help even out the game and make it more fun. Every penny NOT wasted on structures could go into units, produce more action, and make wins more challenging.