For me the line has long been crossed. It's really a binary situation to me, either RL money affects the game or it doesn't.

The attempts by some on the forums to "define" this line for us, using some "logic" to justify their position, are pointless.

What is and isn't "optional" varies from player to player. You are "OK with it" until what you consider "mandatory" goes P2W.

For SE, the line is by and large where they drawn it at that particular moment - i.e. it's completely arbitrary; I suppose if there is a "guiding principle", it would be "will this sell".