Consider attacking a planet-based BS/BATS/SB. At present, one has two options (that I can see, anyway). First, one can close to range 5 and get smoked by ph-4s while trying to beat through extra-strength shields. Even if you win your fleet will be gutted (Tholians excepted). Second, one can clear away any other defenses and approach from the other side of the planet, then launch every shuttle you've got crammed with BP and hope enough survive the base's point-defense fire to land and take the base by ground assault. Considering the die rolls to break into a base and the large numbers of defending BPs, this seems a bit iffy to me... It is possible that I missed a rule that would keep the shuttle swarm safe from defending fire during the turn between coming over the base's horizon and landing (shuttles are assumed to begin atmospheric flight somewhere on the other side of the planet, else they'd be exposed for two turns of fire).
Anyway, given the above, it seems that a device that would allow an attacking fleet to safely land troops by transporter would go a long way towards evening the odds of the ground assault, which if successful would dramatically reduce casualties to the attacking fleet. Three forms of such a device seem logical:
(1) a drone warhead - restricted availability by analogy to the cluster bomb warhead; maybe make a special rule that troopships can take these as general availability. Because of handwavium, each such drone can only relay transporter signals from the controlling ship (seems overly munchkin if one drone could relay from the entire fleet). Obviously these puppies would be easily zapped by the base once they come over the horizon, but the SOP still allows that one impulse in which to make the transporter relay (over the horizon during movement, transport during marine stage, drone zapped during direct fire). Downside: Everyone but the Zin, Klinks, Feds, and WYN would be cranky at missing out on the fun. On the plus side, the Kzinti are supposed to be one of the really good marine races and this fits nicely with that.
(2) Some sort of T-bomb style "mine". I'm not a big fan of mines more complicated than the "go boom" variety so this doesn't really excite me. In principle it makes sense though. Given how few are likely to be available (these would be instead of T-bombs, not in addition) they'd probably have to be hard for the base to destroy once laid, or would have to relay a fleet's worth of transporters to be especially useful.
(3) A new shuttle mission. WWs provide a precedent for lots of powerful electronic junk being stuffed into a shuttlecraft. For flavor, perhaps say that only GAS can be rigged as transporter relays. This one also might be better as a fleet-scale relay instead of just the controlling ship.
As a final note, there are interesting tricks these proposed toys could allow in other situations, for example boarding an enemy ship through a non-facing down shield. However, in the cases of the drone and shuttle versions such tricks should be extremely difficult to set up against a capable opponent, as you'll almost certainly have to launch ballistically. And in the relay mine case, you've taken that in place of a T-bomb which is useful in a much wider array of circumstances. Hmm, to avoid some really stupid tricks this whole idea should be limited such that the shortest path containing the transporting ship, the relay device, and the destination can be no longer than five hexes. It is after all a relay not an amplifier.
Anyway, I think this is a neat and not unbalancing idea. But it's entirely possible that I'm totally off the deep end and don't even know it.
