As a "cheap" way to support playing, perhaps playing the note after 10s would allow you to ear-match the note to confirm whether you got it right or wrong? And just auto play?
Come to think of it, I'd love trainers like this that let me use my real guitars.
As far as I can tell though, the basic advantages of using a guitar, would be that you actually train your muscle memory, by having to fret the note with the correct finger, instead of just visually identifying the correct fret and that you'd get audible feedback in the form of the note actually sounding. The former is, to some extent, possible with the application as it is. I've implemented various modes, but the only one I use any more, is the randomly picked position, which enables certain keybindings, which allow you to turn your keyboard around and hold it like a guitar (I have a split keyboard so I only have to hold up half of it; not sure how practical it is on a normal keyboard). You can then "fret" the keys with the correct finger, which should hopefully build muscle memory as well.
I haven't implemented sound yet, but I'm considering it, so, once that's in place, your suggested functionality would amount to implementing a timeout for each note. Feel free to open an issue request on GitHub.
I think a touch friendly version would be useful for people on tablets.
(I did notice though, that on my tablet the notes aren't positioned correctly, so I'll need to look into that).