Any prospects for more non Democrat or Republican senators?

[ag]

I don't think he'd even have to pledge to caucus with the Democrats, just pledge not to caucus with the Republicans.

A Senator, who is not caucusing with any of the two main parties is entirely useless. Somebody would have to yield him committee assignments, speaking times, etc. If he is truly independent in terms of Senate organizaton, that means his influence is sharply reduced.