Looking back, the new Southwest one is the Research Now version of the SSI singleton site. I use one e-mail address for all the following programs, have for many years in many cases, and totally escaped last year's e-Rewards purge. For SSI, they even helpfully populate your demographic profile when you sign up for a new singleton account with an old address so you don't have to go through the repeat of explaining how you're a Hispanic chainsmoker living in Iowa with a household income of $200K a year and who has three kids under age 18.

The mutiple redemption programs:
e-Rewards
e-miles

The SSI singletons
Opinion Miles Club (United)
Points for Surveys (Jet Blue)
Rewards for Thoughts (BA)
Club Opinions (Accor)
Opinion Check-in (IHG)
Opinion Terminal (Alaska)

The Research Now Singletons (looks similar to the Southwest one you posted)
Jet Opinions (Jet Blue)