I'm not an admin, but I don't think they'll revert back to shields being able to lock players under them anytime soonTM. The feature was abused far more than it was used as intended, and is ripe for further exploitation (griefing and the other myriad forms that pointless harassment breeds), should it be reverted. Additionally, the old feature ended up hurting new players more than any others, and it was (rightly) decided that discouraging new players was in fact a bad idea. So, shields are working as intended in that they keep people out, but cannot any longer be used as planet-sized prisons.
It was never truly intended that they be used as they were to permanently lock people under them, and I doubt that feature will return. In the unlikely event it does, it would be announced on the Sim News.