I don't know if this idea has any merit or not but I was thinking that if the serial comms could be but into a listen only mode and the display be given an address then you could hang multipal displays of the one comms line.
Any way I am having a lot of fun with the display its making life much easier, thank you for such a great product.
If you need to send commands from only one Nextion, you connect TX from this Nextion to RX on MCU.
In addition you connect RX from MCU to TX on all Nextions.
In this example, the text component t0 exists on the three Nextions, whereas t1, t2 and t3 exist on one Nextion only. Button b2 on Nextion 2 is used to send a command to MCU.
Of course Nextion 2 will send an error message to MCU when MCU sends t1.txt="xx" or t3.txt="xx", since Nextion 2 doesn't have t1 and t3 text components.
NB: I have not tested this solution, it is just a concept.