In a thread in the Moding Forum, I mentioned the decal-based shield rendering system, and Bob commented that it could be implimented sooner that one would expect. I do however, have some more questions regarding this, and I thought I'd avoid hijacking the original thread any further.
When this system is implimented, will it completely replace the current pof mesh system, say activated with a command line flag (similar to -ship_choice3D), or will it simply use the system for any ship (indicated in FRED as posessing shields) that doesn't already have a mesh already? Although the first option would probably be easier to impliment, the second would give greater possibilities for campaign designers. For example, your plot involves a capship with shields, whose weakness is that the shield "bubble" gives space so that an attacker can fly though and make an attack at close range. The decal system, IIRC, follows the ship's contours, so such spaces would not exist. If the second solution were implimented, then most ships would use decal-based, but a special mesh could be made for such cases.
While I'm on the subject, I'd submit that decal-shields, once fully introduced, should go hand in hand with FRED check-boxes and/or sexps to override and restore subsystems to a model... if that's possible. For example, in a post-FS2 campaign, GTVA ships get shields, but not until part way through the campaign. These ships require shield control subsystems, which are incorporated into existing warships, once the technology becomes available. Now, instead of having to have 2 models and 2 table entries, one of each with the shield subsystems & hitcount, one without, you would only need one model and table entry. You'd then have a FRED check-box and/or sexps, which would tell the game to ignore that subsystem, the shield subsystem in that case, for that mission only. A sexp to reactivate that subsystem, would allow a mission where the shields are installed in a ship, during the mission.
Finally, as engine subsystems, when destroyed, result in a ship coming to a stop, it would help

if shields (on anything with a shield subsystem) were directly controled by their subsystem(s). If the shield subsystem or subsystems are knocked out, the shields go down. Consequently, if a ship has say 4 shield subsystems and all bit 1 of them are knocked out, then the shields regenerate themselves at a slower rate than if 2, 3 or 4 of them were operative. Perhaps, each subsystem would have a recharge figure, like the wash figure for engines, so that you could have a main generator that has better figures than the 3 other secondary generators.
Man, that turned out longer than I had planned. These are not immediate requests, I'm just trying to get people thinking of this.
Later!