once I change the timing chain kit do I have to change it again over time or will bmw improve the part? Can you tell what improvements they made?

The two major updates are the timing chain crank sprocket which is laser engraved/etched and the oil pump timing chain module has also been updated. Other than those two items other parts like the main timing chain, guide rails, hydraulic tensioner remain unchanged.

what would be the difference between this kit and one needed for an xdrive vehicle?

There are significant differences between xDrive cars and non xDrive cars mostly pertaining to the bottom end of the engine. There is a different oil pan gasket, differential seals/axle seals, axle bolts, bolts for the oil pan, etc. 11318648732KT and 11318648732KT2 are set up with the included items needed to address the specific applications listed. If you have an xDrive car you need to order 11318648732KT2.

Is the Iwis chain included with this kit the updated spec one that was released in 2015 as BMW part number 11318648732?

Yes.

If I go to the part description of the IWIS timing chain, it says it wouldn't fit N26 engine. Is that simply an omission in the description? Given that N20 and N26 are identical for the most part.

Thanks for the heads up. The timing chain is the same for the N20/N26 engine. Fitment on the chain has been updated to reflect that information.

I see the timing chain and crankshaft seal included in this kit are aftermarket brands — why not include the genuine BMW branded timing chain and crankshaft seal in this kit?

They're not aftermarket brands. IWIS is the OE supplier for the timing chain to BMW and is the exact same change. The crankshaft seal is a CFW (Corteco) seal and is also the OE seal sold in the BMW packaging. Most of the other components in this kit are only available in Genuine at this time which is why this kit is configured as such.

Will this fit a 2012 BMW 320i F30 N20 RWD?

The F30 320i is not a 2012 model year vehicle (at least not in the US). It is however available from model year 2013-2016. The kit will fit regardless as the N20 engines are all the same regarding timing components.

Is there a kit for 2013 328i xDrive? Or what additional parts are needed for AWD ?

Unfortunately we have not yet developed a kit for AWD vehicles. This is currently in development and we can publish the differences once an AWD kit is available for sale.

Will this work on my 13 BMW X3 with the N20? The description says no but I don't understand why?

This kit is for rear wheel drive models only.