I’m not visually or spatially oriented, and I don’t know anything about design, but I think Taiwan’s flag should be very busy. It should be like the work of a master Egyptian tomb artist run amok. It should get viewers’ attention, and if possible, visually assault them. Some suggestions:
I think it should have a cornucopia, or an overturned bushel, or something similar in function, containing a rice sheaf, taros, sweet potatoes, sugar cane, peanuts, pumpkins, tea leaves, various fruits, etc. (No binlang!) I think it should have lots of different flowers, too, even the blossoms of the food plants. If you feature a lily prominently, it should have a speck of blood on it.
The flag should contain animal images–the black bear, the leopard cat, the clouded leopard, the barking deer, the mountain dog, purple crow butterflies, several kinds of birds in flight, etc.
The aborigines can be represented by a prominently-located feather as well as the other symbols mentioned in this thread.
The flag should have the sun, the moon, the stars, the mountains, and the sea. Of course there should be prominent symbols of urban life and of industry. The traditional conical straw hat should be featured, to represent hard work and the value of workers.
The characters 國 and 學 should be present somewhere on the flag.
If you can’t fit all that on a flag, you should come as close as possible, and if it’s possible, you should put even more stuff on there. Even if people don’t get it, it’ll get their attention, and they’ll know that Taiwan is about a lot of things, and that there’s something about it that’s different from all the other countries.