Interesting, thanks! Is there a way we could do this without introducing a new function? That is, could something like this work?

ggplot(mtcars, aes(wt, mpg)) +
  geom_point() +
  ggplotly()

Well, I wanted to do so.
I did not do it because the first argument of ggplotly is last_plot().
If it is missing or NULL, we can do what we want by

if (missing(p)) return(ggintearactive())
# or
if (is.nuill(p)) return(gginteractive())

The only way is to add a new argument like

ggplotly <- function(..., layer = FALSE) {
  if (layer) return(gginteractive())
  ...
}