A display without any notches, but with a built-in fingerprint reader instead: Would this still be a possibility - cost-wise and construction-wise?
A second USB-C port will probably be impossible due to space constraints and such, but Audio Adapter Accessory Mode on the remaining port - maybe?
Simultaneously sending 1 audio stream to at least 2 different Bluetooth sinks, complete with latency adjustment and optional Left/Right channel separation: I guess this is both hardware- and software-dependent, but it would be a banger if you could implement it.