Use the W5100 module instead (if you need ethernet)
Good idea, thanks! Same code, but only W5100 based:
Sketch uses 17190 bytes (...) Global variables use 853 bytes (41%)
Using W5500 ( Ethernet2.h ) gives even better:
Sketch uses 14712 bytes (...) Global variables use 809 bytes (39%)
If you don’t need ethernet, use usb or wifi since those options also use less ram.
I need some kind of 25m wire so options are ethernet, RS-485 or PJON
I need only few binary sensors/switches (relays) controllable from HomeAssistant, so I hoped to add their simple logic to
https://github.com/mysensors/MySensorsArduinoExamples/blob/master/examples/GatewayENC28J60/GatewayENC28J60.ino
But building above already takes: Sketch uses 29276 bytes (...) Global variables use 1757 bytes
I tried to reduce SRAM usage, but disabling MY_DEBUG, MY_RADIO_RF24, MY_INCLUSION_* , MY_DEFAULT_* reduces sizes to
Sketch uses 22980 bytes (...) Global variables use 1626 bytes (79%)
only 
Is there any way one can go down with SRAM usage further?
Assuming I have light switch/push button with only readable state (via pin on Arduino).
Following https://www.mysensors.org/download/serial_api_20#sensor-types ,should I present it via:
present(CHILD_ID, S_BINARY);
?
Later, having binary switch (which should be settable from controller) how it should be presented?
How controller can distinguish between RO button and RW switch?