READ BEFORE REJECTING!!!!!
I think cloud chat projects could be allowed under certain circumstances:
1.) They have a blacklist or whitelist that prevents inappropriate words.
2.) Every chat message shows the username of who sent it.
3.) There is a new option for reporting the project called “This is a cloud chat and someone said something inappropriate” where they will be prompted to say their username and quote exactly what they said.
4.) It must keep a record of ALL messages ever sent and never delete anything (unless the list is so big it's reached the data storage limit).
If you think I should add another requirement, please ask.

(1) That's already not allowed.
(2) Most of them already do this.
(3) At that point, you should be sending a message to Contact-Us. The wording of that report option is also loopholeable (although that is anulled due to the ToU stating that the ST may take anything they deem inappropriate for the site down), what if you consistently send a message from the editor (this can only be done by the project creator having added that already of course), or it was something that wasn't “inappropriate”, but something that shares communication details or similar?
(4) There is a limit of 200,000 items on lists, and projects store the whole list within them (as an sb3 is merely a glorified zip file (think a DOOM WAD, if you will) - It contains every asset and data of sprites, lists and variables within it), and there is a memory cap - I don't think that'd be possible.

The only form of cloud chat that is allowed is Preset phrases (Like “Hello!”, “So close!”, etcetera.), but not unrestricted ones, blacklists (those can easily be bypassed and people looking inside the project will see it. This applies to using the Translate extension as a filter.) and a whitelist.