i3 doesn't have any keyboard configuration options, so... unless you're just talking about keybindings, which you can totally reconfigure in Sway and reload without restarting. What you can't do in either is set the keymap on the fly without restarting. This is something you can do on i3 but it's an X thing, unrelated to the i3 config. On sway you can configure multiple keymaps ahead of time and switch between them without restarting, but cannot change the configured keymaps on the fly.

Changing your keymap at runtime is something we hope to have in sway 1.0. We'd also like to support multiple keyboards with different keymaps and even configuring which keymap you use on specific windows.