I just found this project while searching for an alternative for i2cssh for Linux (Tilix in my case).
One thing I'm missing from csshy is that I can't pass any custom SSH options to the spawned SSH processes.
In i2cssh, it is possible to pass custom SSH options using the -X option (e.g. -Xi=myidentity.pem).
Maybe you could add such an option to csshy, too.