No offense, but, can’t we get past that way of thinking, yet? Don’t RQ6, Legend, Magic World/BRP, OpenQuest, HeroQuest, SPQR, and GORE already all “undermine” each other? People play all these. People also play OOP games like MRQII and Avalon Hill RQ3. People also play less-related games like Pathfinder and GURPS and a million other RPGs. They’re all designed to cater to different tastes. WOTC has learned that suppressing old editions doesn’t help the popularity of a new edition; that the new edition must stand or fall on its own merits—i.e., it really has to be BETTER in order to be competitive, not just in-print.
In other words, if they did a RQ2 limited reprint, they might make a buck off it from the people who want it, but if RQ6 is really superior it won’t hurt RQ6.