On my dev system i have a build of fiddle which uses the jquery.terminal plugin as the main interface (with a button to toggle between it and the current UI), but it relies on 3rd-party code which is not approved for inclusion into the core sqlite3 repository (plus it's huge: all of the competent terminal-like APIs we evaluated so far bring 300-500kb of minimized JS dependencies). Reimplementing such a console, minus the jquery/etc dependencies, is beyond my current ambitions but has not been ruled out entirely long-term. Baby steps.
> bundle various $EDITOR choices
That would require a _proper_ terminal for those editors to live in, as opposed to a terminal lookalike such as jquery.terminal. xterm.js could presumably do it but is even bigger than jquery.terminal. No doubt that's _possible_ in wasm, but such features are _way_ beyond any current aspirations or scope for this app.