As most YouTube playlists seem to be updated at their start, it would be quite useful to play those playlists, on a PC or in the Android Go app, in reverse order. I would also be interested in the reason why playlists are updated like this, as there has to be a reason for it!
I ran into a site that seems to do exactly what you asked for: https://playlist.tools/
It allows reverse playlist playback and doesn't need you to install any browser extensions
You can play it in date order from oldest published to newest using this site: http://www.playbackloop.com/
But I am still looking for a way to simply reverse order
This guide is for chrome users.
I am using this solution right now so I can confirm that it works.
Step one: Download the "Reverse Youtube Playlist" chrome add-on. (The add-on was last updated in 2014, but if you follow these steps it will still work)
Step two: Go to the youtube playlist that you want to reverse and add this to the end of the URL: &disable_polymer=true.
So your complete URL should look something like this: https://www.youtube.com/watch?v=M1nd8WPZO_c&list=PL34C1F26D03F5F9B8&index=94&disable_polymer=true
Step three: The playlist bar should now look slightly different. You will also notice that there is an extra button on the playlist bar with a down and up arrow. This is the button to reverse the playlist using the add-on you downloaded earlier.
Clicking this button should reverse the current order of the playlist. The reason you need to add the text to the URL is because the add-on only works if you are using the old version of youtube.
If youtube decides to take away the old version this solution might stop working.
That is the solution. Enjoy
Yes, with a Chrome extension called Improved YouTube!. It's open source and supported on GitHub. Some settings can be somewhat buggy at times but overall it is wonderful. Install it here.
Then go to Improved YouTube! Settings → playlist → enable reverse.
Ive figured it out when you are on your playlist add &disable_polymer=true. to the end of your url then install the extensions "reverse youtube playlist" and "Improve Youtube! (Open-source for youtube)" then pin and click on the "Improve youtube" extension then click on playlist then click "reverse" and then there will be a black "up and down" button on the youtube playlist you want to reverse and it will reverse