I hate smart ar*e postings but the comprehensive answer to all this is this:
Class G Airspace is a free for all.
A lookout doesn't really work (despite all the ex RAF navigators revolving in their graves at 2575rpm as I write this) because a target on a genuine collision course will be a stationary point in the sky.
And a 421 is not going to be doing 100kt.
The only hope of a real solution is unfortunately technological, but is totally undermined by those who are against transponders.