I like the choice of Lua and SDL, not only as a modern LOGO/BASIC alternative. I think it can go much further.
I guess as a minimum you want the editor to function to the level of notepad/pico/nano, and then perhaps have helpers with regards to indenting, and after that error marking similar to that of QBASIC, and after that syntax highlighting.
I guess as a minimum you want the editor to function to the level of notepad/pico/nano, and then perhaps have helpers with regards to indenting, and after that error marking similar to that of QBASIC, and after that syntax highlighting.