Really? I feel like if you have to ask what plugins to build you’re doing it wrong. You should know what plugins to build by being a user of Datasette and understanding its limitations for your self.
I know Datasette better than anyone else, and I still couldn't come up with 40 useful ideas in less than a minute.
Once you have an AI to also prototype the plugin ideas, such an idea list may become useful. I've always seen that the owners of any product have more product improvement ideas than they could economically implement.
I asked GPT-4 to implement a simple plugin yesterday, and the code was 90% right out of the box.