Can I install openwrt on my deco e4 router?

I want to install openwrt on my deco e4 router. Is it possible?

No, this device is not currently supported.

Will it ever come?

I don't know.... someone would need to have the device and be willing to start development for it. That someone, at this point, is you... the process is outlined here:

https://openwrt.org/docs/guide-developer/add.new.device