Hmm... closest thing i can think to this would be a Sap that moves from point A to point B, and needs a supply of energy via energy transfers to fill its "accumulator", with this above 50% the sap would move at max speed, say 40-50kph, the defenders or enemy could hinder this by using neuts/drains/damage on the sap.
Also without energy in the accumulator, it would have no shield, and be vunerable to destruction, and move back slowly, give it 10-15K armor and 50% resist or something, at which point a new sap spawns at point A, maybe give it a cooldown of 1 minute or so.
The only difficult part i can see is deciding who gets credit/ownership.
Maybe some win conditions could be like.
Corp A get the Sap 60% of the way Corp B get it the other 40%, corp A wins,
Corp A gets the sap 60% of the way, Corp B wait until the sap is back at 30% and take it the 70% of the way, corp B wins.
or
Whoever gets the Sap to Point B and "Activates" it, wins.
(Only just come up with this while reading this topic, so its probably not perfect)
Overall, i would definatly like to see some more varied and interesting SAP types in the future.
Anyone who has played games like TF2 or Global Agenda know the kind of gametype this resembles, but usually they work with a fixed attacker/defender.