Anytime you have a question about what Jeep or any Chrysler product for that matter, is planning I suggest checking out http://www.allpar.com/ These guys have always had the inside scoop on what is happening behind the scenes and were also the first to post Chrysler's 5 year plan.
Now to answer your question...no there are no plans to put a Cummings diesel into a Grand Cherokee, actually there never were. The 3bt, the baby brother of the the larger pickup diesel engine, is still a bit to big to stuff into the Grand Cherokee without some major modifications. There are a few write-ups on the internet were people have done them but all of them could not use 4WD due to the size of the engine and transmission associated with it. So they had to take out the transfer case to make room. I also believe they had to lower the motor by 2" to get the hood to shut. Anyway...it has been done but it is not easy my any feat, and because American's have long been opposed to Diesel engines they won't look into engineering a fit. The Diesel motor that was in the Grand Cherokee was only available in the US for the 2007 - 2008 model years and has been dropped due to the fact that the sales were so low. To give you an idea of what I am talking about the Diesel was an option in Europe, Asia and Australia from 1999 - present. Approximately 13,000 are sold a year and out of those less than a 1,000 were sold in the US. Here is what allpar has to say about the 2011 Grand Cherokee, the next model redesign is not expected until after 2014 "Outside the US, the 2011 Jeep Grand Cherokee will, as in the past, be sold in left- and right-hand drive with either diesel or petrol engines. The diesel engine was to be the Mercedes 3.0, but “Stratus” told us that was yanked in September 2009. Instead, the Grand Cherokee will (he said) use VM Motori’s brand new RA 630 DOHC engine, another 3.0 liter V6, with four valves per cylinder and common rail fuel injection; power output is estimated at 247 hp (184 kW) with torque of 369 lb-ft (500 Nm). We'd expect the transmission to stay the same." http://www.allpar.com/trucks/jeep/2011-cherokee.html
The same goes for the Wrangler..its been talked about but basically there is not enough interest from the buying public.