If circular economies aren't established before the arrival of CBDCs, it will be much more difficult for people to acquire Bitcoin.

Shitcoins pose a threat in the sense that people falsely associate "Bitcoin" with "crypto". The blowups of Luna / Celcius / FTX had nothing to do with Bitcoin, yet the regulation in response to this will no doubt attack Bitcoin users (Warren's proposed bill being the latest example).

A popular talking point is how Bitcoin will perform with a low block subsidy. I don't have much of an opinion on this and am waiting to see how fee markets develop over the next decade.