Hi,
discussing or directly attaching something using Playroom's servers are two very different things. Of course, as per the rules, you aren't allowed to discuss it either, but your private chats remain private. On the contrary, there are nowadays DMCA bots that work by analysing hashes of every uploaded file and flagging the material if it's copyrighted, which could go into some serious and quite unnecessary trouble.
IN the end, the one to decide is the developer himself, and if it can be assured that no problems can be caused, why not, I am not against the idea, just mentioning a possible issue that can in fact be quite serious.
As for good temporary upload sites, there are places like https://1fichier.com or https://uptobox.com
Usually they aren't too restrictive and allow you quite large file sizes, with the note that they often as I already said are time limited links.
However, nowadays also you get many very good free cloud storage files, for example OneDrive 5 GB or Google drive 15 GB, so you can practically get 20 Gigabites for sharing without paying anything which isn't bad at all. You will however notice that even they as big companies won't allow you to add copyrighted content, and depending on how popular a certain file is, your links could very well get banned if you share something problematic, so I advise you to be careful there as well.