Is your feature request related to a problem? Please describe.
No, the spigot plugin sudo allows you to chat as another player though

Describe the solution you'd like
The command /doas to have the "subcommand" /doas [USERNAME] c:

Describe alternatives you've considered
Using the doas command and then making the player execute the say command, but that does not work very well

Additional context
For example /doas John c:Hi would make the player John say "Hi"
2nd example /doas John c:Hello there would make the player John say "Hello there"