I think that you still need capacity planning for "serverless" architectures as well. You need to forecast growth of usage and costs for accounting and budgeting purposes. Does your serverless usage scale linearly with new customers? Or new widgets on the platform? Great, if we're planning on adding 10,000 widgets to the platform next quarter how much will our serverless bill go up? We still need to think about these things.

Also, and this may be my lack of experience, there seems to still be a big requirement for more traditional cloud hosting for databases in a serverless architecture. You have to store that state somewhere.

Going serverless would increase your costs significantly. Have you seen how much AWS charges for Lambda use? Where did this myth of serverless saving you money come from?

For general compute yes. But you still need to scale your persistent data stores. That is why AWS is investing in things like Aurora. Also you need to understand where to optimize on a cost basis by not just profiling code, but comparing costs, to usage, to performance gains in reduced resources needed.

Serverless means to pay somebody for runs the server.

Serverless is more server and its funny.