I feel like the people who are going to watch the newest season are going to watch it, and those who aren't just aren't. I know that sounds like a stupid sentence, but it's true. At this point the show has been on so long that you're either into it or not. If you've never seen or heard of it before, you can always check out the first season pretty easily on streaming services to see if you like it, but there's also no reason not to jump right into the new season since it's not super serialized.
It may be a good time for old fans who fell off after season four to get back into the show. Although some people may be tired of the Always Sunny schtick, the cast still has plenty of laughs to give.