The timing of -- officially made on Wednesday -- is a bit intriguing, though.

For maximum political bang, the SEC has good reason for wanting to implement it in time for the first anniversary of the May 6 market meltdown. The 21-day comment period would give the agency just eight business days to meet this timeframe. After the comment period, the SEC has said it would "then determine whether to approve (the proposal) shortly thereafter." But, of course, this week's proposal came just ahead of the deadline for a possible government shutdown --- perhaps as early as tonight.

The proposed "limit up-limit down" mechanism would prevent trades in listed securities from occurring outside of a specified price band -- a band set at a percentage level above and below the average price of the security over the immediately preceding five-minute period.

For stocks currently subject to the "circuit-breaker pilot" installed shortly after last May 6, the band would be 5%. All others would be given 10%. The percentage bands would be doubled during opening and closing periods, and broader price bands would apply to stocks priced below $1.

If the new proposal wins approval, all trading centers -- including exchanges, ATFs and broker-dealers executing internally -- would have to establish policies and procedures "reasonably designed to prevent trades from occurring outside of the applicable price bands, to honor any trading pause and to otherwise comply with the procedures set forth in the plan."