After my post with the comment sorting script yesterday, I thought that since I was already doing script rewriting I might as well go further, so here is a script implementing infinite scrolling for the home page and communities on Lemmy.
I didn't publish it as a separate script to comment sort since both are incompatible, as they both edit lemmy's client.js. If sorting comments by Top annoys you, just change the defaultSort back to Hot in the script.
Edit: Fixed the spinner on instances other than lemmy.world.
I can see options to change the theme, type, sort type (for posts) and show NSFW content, but there are no options to change the sort type for comments as this script does.