Let us assume:
- That there is an equity premium (
[PDF]UPDATE: Link modified to Brad De Long posting in which the PDF is embedded. Hat tip: Don Lloyd in comments.)
- That the equity premium can be derived from a linear relationship (y = ax(1) + bx(2) + ….) of the most significant variables.
- That equity premia are, to some not-insignificant extent, based on Wealth Inequality [PDF].
- That one of the primary variables contributing to the premium is the reliability and quality of the information provided
If so, there are two possibilities. Either,
- the firms are perceived to have a higher present value, despite the change being one of accounting, not business flows or
- the stock prices decline in the face of greater uncertainty, leading to an increase in the premium due to a lowering of the price.
My instinctive answer—which I can probably be convinced is wrong, but it would take some effort**—is that the second would be the result. Leaving only one question:
Why does Christopher Cox (R-CA) hate the Securities Markets?
*Following from  above, we can assume that greater information tends to result in more optimal investment practices, and therefore a lower equity premium.
**The argument would have to show that the loosening of accounting practices will result in improvements to the company’s business processes that would not otherwise occur.