Things get funky with emojies, and as I wrote about earlier, Discourse isn't really well-optimized for formal, long-form writing. I think that can be alleviated by giving the option of line spacing. Sure it'll look a bit weird and make long posts appear longer, but the extra spacing can help as a reading aide for people who need that.
If there is no way for anyone who manages the Discourse software here to do that, then I'll fabricate a solution myself for users of Stylus or ViolentMonkey.
I'd discourage really long posts in general as they have the tendency to become waffle, or could be perceived as rants that didn't contribute much value to a particular topic.
While we could change the line spacing (line-height) through styles, I don't think it would be necessary to do considering the day-to-day topics/posts. Plus it might have an adverse effect -- I know I'd find longer line spacing harder to process. 
Instead, consider reducing the content of such long posts, or use a browser extension if it helps. A quote from Pythagoras I remember is:
Do not say a little in many words but a great deal in a few.