If you mean your proposal adds more things, that sounds like it might be over-complicated. To solve the problem of tightly-fitting boxes around terminal text -- if you consider that to be a real problem -- overstrike sounds like a really elegant solution.

Which things do you consider in your experience of writing tuis that are mentioned as being wanted in the blog post / rationale doc linked to be unnecessary?

If you want those things then overstrike is insufficient.

cell borders sound even more elegant imo, they are a targeted, precise fix for a useful feature. overstrike sounds messy to me though I can see where it has a lot of uses.