One thing I've noticed about Greggman's HTML5 Bytebeat is that instead of simply setting

window.location.hash

(which would add a new entry to the history), it uses

window.location.replace()

to change the URL without adding a new history entry. This method updates the URL without creating additional entries in the browser's history stack, whereas Dollchan does

window.location.hash=`#v3b64${btoa(String.fromCharCode.apply(undefined,deflateRaw(JSON.stringify(songData)))).replaceAll("=","")}`;

every time you type a character which is annoying ('cause it floods your history). Besides, there's also

window.history.replaceState(null,"",URL)

…
On the other hand, could there ever be MIDI/keyboard input for playing notes in real-time? Or the ability to import audio samples (could also be raw data too for any arbitrary file) being read as arrays without having to encode them into massive strings? Maybe even microphone input for implementing effects?