If I have printed with a PEI sheet and then want to print with a cool plate I notice that the pritner wont start until the bed cools down.
I think there should be an alert that state “Can’t print until bed cools” or “waiting for bed to cool to start”
That’s an interesting thought, but I think your idea will be a non starter.
This is the standard way every 3D printer works. The machine must wait for many conditions for each print. The Bed and Nozzle temps go up and down many times during the process. There is no need for additional warnings, just wait. 
I’m not being an a$$ 
, but it’s not needed and won’t be added. here’s why:
The Firmware has a limited space (memory) in the printer. Any messages or routines to be added at this point are carefully considered as adding one can break other things, and might use the precious space that’s needed for an important update or improvement in the future.
There’s no reason BL would add this as it’s a normal function that all printers go through.
Cheers!
I service uptier 3d printers. If i try and run a bed level after a print it will tell me.
“Can’t perform the action, Nozzle too hot”
So this is something in the industry. You printer is targeted at users who have less experience with 3d printers. Leaving this message out is UX issue. Users, like myself felt that there was something wrong with the printer. Further more this message doesn’t need to come from the firmware it can be in software.
Just like you have a message that says “the board markers are not present. Printing can’t continue”, you can easily add a information / warning alert stating “Bed is too hot. Printing will begin when it cools down”
I bow to your knowledge, one of the problems with these forums, you never know what level to speak to a person. 
True, but the majority of such messages on this printer are in firmware so the user doesn’t have to go back to a tablet, phone or PC. This sort of message would be displayed on the printers screen.
BTW - for the record, I totally agree it would be a nice message, I personally would like it!
As for your suggestion - I’m not sure how much BL watches these forums for suggestions. I do know there’s some BL Staff watching things, but …
The proper channel for your suggestion if you’d really like it to be seen is here:
It will get much more attention than here.
Nice to meet you ilan.perez !!
Cheers!