The new criteria for what makes a blade acceptable for SCA Rapier and Cut & Thrust combat is now posted on www.sca.org, which makes it an official rule, effective now. See http://www.sca.org/officers/marshal/combat/rapier/
Most blades currently allowed are expected to flex appropriately to continue to be allowed.
Kingdoms can still place additional restrictions on which blades are allowed.
Changes to the official rules/handbook won't happen for a few months, but the new text posted on the website supersedes the posted document.