A means of being able to shoot out of our boats after Falling Back. Also, a potential means to wrongfoot your oponent.

1.The Shooting Idea:
A Raider or Venom is locked in combat with an enemy unit.

The Embarked unit gets out, moving to the maximum distance of the 3" bubble in the direction you want to go.
"...can Disembark before the transport moves."

The transport then falls back in the same direction, trying to position such that the unit will be able to end fully within the 3" bubble to embark when the unit next moves.

Move the unit into that bubble, the unit has ended its movement within 3" of the transport. And thus they may embark on that transport.

This reduces the amount the transport can move to 10 or 11 inches, but I don't think it gives us anything.

The "open topped" rule says nothing about units being allowed to disembark or not. The open topped rule says that any unit embarked in a turn when the transport has fallen back cannot shoot.
I'm pretty sure that blanket-covers it, but what do you guys think?

2. The Wrongfooting Idea:
Similar to above, but making use of two Raiders (and their occupants).

Assume we have a Raider filled with 10 Wyches. This is Raider 1.
Assume we have another Raider filled with 10 Kabalites. This is Raider 2.

Raider 1 and Raider 2 move up the board, Raider 2 gets a turn 1 charge, Raider 2 does not. Both Raiders stay within 10" of each other, despite the charge.

Assume the oponent decides not to fall back with their unit.

The Kabalites disembark from Raider one, straining at the bubble towards Raider 2.

Raider 1 Falls Back. The Kabalites move towards Raider 2, potentially advancing to get in the bubble of Embarkment.

The Wyches disembark from Raider 2 and Advance towards the enemy unit that Raider 1 fell back from.

The Kabalites embark on Raider 2. Raider 2 moves away towards another target.

Raider 1 shoots something, probably an enemy tank.

The Wyches shoot the previously locked up unit before the Wyches charge.

Raider 2 and the Kabalites now shoot at their new targets.

The Kabalites have just netted a 24" relocation.

The Wyches have just netted a charge.

Raiders 1 and 2 have separated and are now able to shoot at their preffered targets.

The opponent now has the unit they were expecting to be freed up because it was facing KABALITE WARRIORS is locked up once more (this time against Wyches that can potentially cause it harm, but will maybe tarpit it for a third turn even if the opponent tries to fall back.

YOU get to laugh like the Joker and declare "Just. As. Planned!"

A similar maneuvre could be used to swap units around mid-battle for threat relocation, though if neither Raider has charged, then you could swap shooting units around and re-embark on either side of the exchange.

Say Trueborn swap with Warriors to point the Blasters at a live tank and the Warriors at the exposed Infantry from the previously popped tank.

Or put Incubi in charging distance of Marines whilst Wyches square off against some Guard.

Debatably useful, and potentially situational, but I think it could be fun to use.

You cannot embark and disembark in the same turn.

Well that blows a hole in everything.

Actually, where is this stated? I just read the Transport rules (blue text bubble, same page as Morale rules) and it makes no mention of embarking and disembarking in the same turn.

Is this another case of "everyone knows you can't put Hellions in a Venom."

Nope, this is no such case.

Actually at the end of the 1st paragraph of the transport rules.

It says (roughly translated from german):
Keep in mind that a unit can not embark and disembark in the same turn.

Yep, my bad.

Ah well, 24" relocates will have to be found another way.