`spec_guess_object()` does not work for non-vector elements

[mgirlich]

model <- lm(Sepal.Length ~ Sepal.Width, data = iris)
tibblify::spec_guess_object(list(x = model))
#> Error in `.f()`:
#> ! Input must be a vector, not a <lm> object.

^{Created on 2022-06-20 by the reprex package (v2.0.1)}

But tibblify() works with the following spec

spec_object(x = tib_list("x"))

Does tib_list() really make sense here?