I do not want to see this implemented, Tommy. Here is why:
I think such a thing against cleaners will remove the naturalism of the gamemode on Cubecraft. Skywars has been just a standard gamemode for a long time, and adding such a big change is a risk.
Also, this is already featured on Hypixel, and I think Cubecraft should be different from Hypixel, so people can choose on which server they want to play by their play style.
That does not mean that you have to die by cleaners all the time. Rushers are very annoying as well by the way, as they are often cleaners as well... Preventing cleaning is possible by thinking before you attack somebody, Use your strategic mind. If you are left with two other players in a map, for example, it is smarter to not attack but wait for the other two to fight. Most cleanings could be prevented by just using your strategic mind.
I am a cleaner - not always, I clean sometimes, when it is just stratgically smart. Why would you put yourself in a 1v2 if you could just wait a few seconds and look behind you to prevent you being backstabbed? I like such a strategic twist. Also, if the cleaners are really worse than you in pvp, you should also be better in strategically thinking. Otherwise, you just deserved to be killed by him/her.
Cleaning also speed up gameplay.
What I do not like, are campers. Camping and cleaning are different things. A camper who is making a skybase is very annoying, but luckily, that is already forbidden.
You can always use the speed potion kit yourself to prevent cleaners as well if you have some difficulties with strategy, that way, you can throw a speed potion on yourself three times, and it is a very underrated kit.