What might come after Bluetooth for wireless headphones?

Bluetooth may just keep evolving rather than being replaced outright. Newer versions have improved bandwidth and latency, and more efficient codecs can make better use of the available connection.

That doesn't guarantee lossless audio or minimal delay on every pair of headphones. The codec and the devices at both ends matter too.

For headphones, I wouldn't treat bandwidth and latency as the same problem. A connection needs enough sustained capacity for lossless audio, while delay also depends on encoding, decoding and buffering. A faster radio alone doesn't necessarily fix both.

Wi-Fi is another wireless option with more bandwidth, though that doesn't automatically make it a drop-in replacement for Bluetooth headphones. Power use, device support and latency still matter, so the best connection depends on what you're trying to do.