Mitchell L. Engler (Cardozo) has published Progressive Consumption Taxes, 57 Hastings L.J. 55 (2005).  Here is the Conclusion:

The X-tax and the Hybrid Approach took different paths to their overlapping recommendations for a progressive consumption tax. The X-tax reacted to the conventional VAT’s lack of tax-rate progressivity; the Hybrid Approach addressed revenue, transition, and tax avoidance concerns under the traditional cash flow tax. Together, these two independent proposals reinforce the merits of implementing a consumption tax, in part, through a progressive wage tax. The further overlap between these two independent proposals underscores the importance of a supplementary tax on consumption less wages. In addition to raising revenue and protecting the wage tax base, such supplementary tax highlights the serious flaw in the traditional assumption that a consumption tax comparatively exempts all investment return.

Moving beyond their shared characteristics, a comparison of these dual consumption taxes highlights important differences. The X-tax makes a number of significant structural changes to current law, intensifying potential transition and related objections. In contrast, the Hybrid Approach favorably works within the current framework, changing the current individual tax only to exempt the risk-free return and eliminate the capital gains preference. Both changes target the loopholes arising from the realization requirement, long recognized as "the Achilles Heel of the Income Tax." On the other hand, the X-tax furthers the administration of the consumption tax by limiting individual tax reporting to wages.

My refined proposal combines the relative strengths of the X-tax and the Hybrid Approach. First, the current entity-level tax on corporations would be maintained, modified only to allow a risk-free exemption. Second, a low-rate shareholder dividend tax would be maintained as well. Despite its designation as a shareholder tax, this dividend tax could be calculated and collected by corporations, like the corporate-level tax. Finally, the exemption of designated investments from the Hybrid Approach’s individual investment tax further enhances the administration of the tax. These critical, yet concentrated, changes ease the way to a more equitable, efficient, and administrable consumption tax.