Looking at element_geom, I noticed a couple of things:

1. linewidth/linetype and borderwidth/borderwidth doesn't seem internally consistent.. See example code below. Not sure how to fix this..
2. Likewise, I think it'd be more intuitive if argument names in element_geom names would map to aesthethetics as much as possible. So I think pointsize sould instead be size etc with a separate element_geom_font function.

library(tidyverse)

p <- ggplot(economics, aes(date)) +
  geom_density()

#would expect this to work
ggplot(economics, aes(date)) +
  geom_density() +
  theme(
    geom.density = element_geom(
      linewidth = 5,
      linetype = 3
    )
  )

#given you can do this
ggplot(economics, aes(date)) +
  geom_density(
    linewidth = 5,
    linetype = 3
  )

#instead have to do this
ggplot(economics, aes(date)) +
  geom_density() +
  theme(
    geom.density = element_geom(
      borderwidth = 5,
      bordertype = 3
    )
  )

#but you can't do this
ggplot(economics, aes(date)) +
  geom_density(
    borderwidth = 5,
    bordertype = 3
  )
#> Warning in geom_density(borderwidth = 5, bordertype = 3): Ignoring unknown
#> parameters: `borderwidth` and `bordertype`

^{Created on 2025-06-17 with reprex v2.1.1}