I have a 2000 CLK 320 with a 722.618 which experiences a harsh hot P -> D engagement. It has fresh correct fluid, new connector, dry TCU, all the usual stuff...

When cold, engagement of Drive is buttery smooth! It builds up the pressure very gradyally, I barely feel the engagement.

At operating temperature it sort of slams it in, I'd best describe it as if I raised the engine RPM a bit then put it in Drive. The car feels like it's beeing bumped from behind, very uncomfortable.

I found the LI27.50-P-049281 adaptation procedure for the 7G-tronic which calls for shifting P -> D a bunch of times, doing some waiting and warming up. Doesn't work on the 722.6 unfortunately.

Is there a specific 722.6 procedure for adapting P -> D engagement?

That procedure only applies to the 7G tronic.

What you are experiencing is quite opposite of what normally happens with older 5G tronic. When these get older the torque converter clutch starts to grab when cold and you get a dead slam garage shift (P to D) and a strange yanking feeling when you let go of the brake. In worst cases the car stalls out as soon as the geartrain engages.

I think you are experiencing a sticking apply piston or a warped steel plate in one of the clutch packs, Sometimes a sticky piston can be nursed/helped with a small dose of additive/conditioner in the transmission fluid.

However, you may also be experiencing some noise in can-bus system or even oil migration in the TCU which again can cause noise in the bus. Does this happen when the car is left in the sun for a while? (the shifter is also part of the bus network which can cause this situation of slamming into gear at full pressure)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Nope, not related to ambient temperature. The car can be baking in the sun the whole day, but as long as the fluid is cool, it will engage perfectly.

If the problem is as you say a "sticking apply piston or a warped steel plate", is there any other up/down shift that uses the same component as the P > D? Maybe I can look for sympoms there?

One issue the transmission has is sporadic harshness in some shifts, I believe caused by sprag issues. My heavy right foot takes credit for that

Could a failing/failed sprag cause the P > D harshness? If so, why only when hot?

I would see if there are any fault codes in the TCM. A fault for the turbine speed sensor can cause a harsh engagement from park to drive or reverse. Usually its a bad conductor plate.