Toward a More Responsible Two-Party System

I thought the point made in the "Toward a More Responsible Two-Party System" essay about disciplinary action versus positive incentives was a little confusing (page 21). It seems that the authors suggest that there can be disciplinary action only as a last resort for party disloyalty or the like, and that it is better to rely on positive incentives to keep party members loyal and productive. But what would those incentives look like, if they are different from what we have now? And if we did have disciplinary action, even as a last resort, what would that be?