As a Cubed player, I've spent time on the server and spent money to be trusted and have the ability to upload custom plugins. What prompted me to cancel my MVP payments in the first place is that I couldn't add custom plugins, even though I should be trusted to not cause any security issues.
Although I’d like to have custom plugins on Cubed, the money you have nor the time you spend determines your actions. Anyone can change their mind at any time for any reason; such as someone getting banned, quitting Minecraft and they don’t care anymore, or other reasons. It would be much better if Party just secured everything and added supported for it.
Trust isn't the issue here. Cubed does trust some people but not enough to cause "security issues". From what I understand, they do want to support custom plugins, but underlying problems with the PlayerServers platform make this impossible, which is also why there are no plugins that can read/write files. Now with partydragen more focused on cubed however, we may see some improvements towards this, but don't get too excited as it'll probably take a while