Closed betas, a relatively recent addition to City of Heroes issues, are a pretty mysterious business. For a start, nobody knows exactly what the selection procedure is. You can even be picked for closed beta for one Issue and not included next time around. As there's often at least a few weeks between closed and open betas, the closed beta testers get a serious head start on checking out the new awesome. As well as doing some serious focused testing, of course.
However, now closed CoX beta access is being offered as an added perk of attending HeroCon. Whether this will include Issue 13: Architect is not certain: 'Given the timing of Hero Con this may include Issue 13 closed beta, but will also include access to the future closed beta of Issue 14!' This is on top of the permanent Carnival of Shadows Harlequin costume power.