Official arrival and berthing photos. They offer some excellent views of the mysterious white panels and uncovered MLI section. I'm 99% sure that brickmack is correct here, NG happened to release a video with renders a few days ago and the panels aren't a perfect match but they definitely look similar. The MLI-only section is where the unpressurized ISS hardware will be attached for disposal.
https://www.flickr.com/photos/nasa2explore/
Thanks for sharing that video with NG's official renders of their Gateway module (apparently now called "HALO" i.e. Habitation and Logistics Outpost) and deep-space Cygnus! Been wondering for a while how they were going to evolve Cygnus to deal with the challenge of needing docking ports on both ends. It's cool that they took advantage of that design (with the new outboard OMS engines) to also allow unpressurized cargo delivery on the deep-space Cygnus.
(Gotta say though, the music in the video was trying a little too hard to be epic.

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I've been pleasantly surprised by how proactive NG/OATK has been at incrementally evolving their various assets (Cygnus, MEV, and even their SRBs with OmegA, although the jury's still out on whether that'll be much of a success) to stay relevant in a rapidly changing space landscape. Of all the "old space" companies right now (with the exception of Sierra Nevada, who's technically "old space" but doesn't act like it), they seem to be most aware that waiting for government funding to pay them to so much as sneeze is a recipe for getting left behind. (
*cough* Boeing *cough*) I found it noteworthy that in a roundtable discussion amongst SLS contractors a year or two ago (wish I remembered where it was...) they were the only ones telling the rest "hey, we should be thinking past the lucrative development-phase gravy train and planning for serial production", something the others seemed uninterested in hearing. Meanwhile they've been quietly taking the assets they have and building them into clever new things that are far enough along to win contracts while their competitors are still in the PowerPoint phase. Blue Origin could learn a thing or two from them about "gradatim ferocitur".

Cygnus has been the best example of this. First they added external cubesat deployers to capitalize on the burgeoning smallsat market. AFAIK that's all been a private enterprise (partnering with NanoRacks and the like) - hitching a more or less free ride on already-paid-for NASA CRS missions to launch cubesats for very little marginal cost. Then they added the SlingShot deployer on the front hatch for even more cubesat deployment flexibility. Around the same time they started extending the duration of Cygnus missions - first just seeing how long they could keep one up there after leaving the ISS, then adding reaction control gyros to make the station keeping fuel last a lot longer. Now they've got two of them up there at the same time to prove out their ability to handle that in mission control. All of this has been on missions already paid for by NASA, after the primary mission was over - a lot like how SpaceX developed first-stage reuse on the cheap (they could afford to lose a lot of boosters because they'd already done their paid-for job).
When I heard that they'd been given a sole-source contract for the Gateway hab module, on the basis that they were the only contractor who NASA saw even being close to delivering on time for 2024, I realized how this gradual investment had paid off. None of their competitors were ready because they were waiting for funding before actually bending metal. Meanwhile NG already had an active production line for Cygnus and a credible plan to straightforwardly evolve it into the needed Gateway module (HALO).
I then guessed "hmm, we'll probably see Cygnus starting to look more and more like HALO between now and 2024" and sure enough, NG-12 shows up with the same radiator panels shown in the HALO renders. I wonder what we'll see on NG-13 and NG-14. My guess would be they'll replace the berthing node with an IDS-compatible docking port and try automated rendezvous and docking sometime soon. They've already done most of the hard work for automated rendezvous and docking with the MEV (Mission Extension Vehicle) project; MEV-1 was launched recently and is on its way to dock with an old GEO comsat. Docking to the ISS/Gateway is a little more complicated due to the complex rules and need for human safety, but again, the hardest part has been done. Building the IDS port itself doesn't seem too hard - SpaceX and Boeing have both already done it and we haven't heard either of them complain about it ever being a "long pole in the tent" for Commercial Crew.
IIRC, NASA set a target time frame of 2021 for their proposed commercial node module to be added to the ISS at Harmony Forward. 2021 would be crazy aggressive for that, but I can see why NASA would want it that fast, because the IDAs are going to get crowded as private crew and cargo flights pick up. NG is the only company I could see being able to deliver such a node that fast (except perhaps SpaceX, but they're not really interested in that). It would be basically a clone of their HALO module for the Gateway, except simpler, because it can rely on the ISS for things that HALO will need to do on its own (life support especially; also there's no need for xenon propellant transfer to the PPE from visiting cargo vehicles). It would make a lot of sense for them to do an ISS module first in 2021-22 as a "dry run" for HALO.
Heck, once they've got IDS ports and automated docking on Cygnus, there's all sorts of fun things they can do in the post-mission phase. With androgynous ports they could dock a couple of them together and declare it the "first private space station". Not much of a station (and it wouldn't be permanent), but it'd get them in the history books and put them squarely in the lead in the race to a commercial station to replace the ISS. If they wanted to get really fancy they could switch to the new HALO/deep-space-Cygnus service module that lets them put a docking port (with no pressurized pass-through) on the aft end in addition to the main front one, allowing two Cygni to dock together while leaving their front ports free. They could then contract SpaceX or Boeing to have one of their Commercial Crew missions swing by the "Cygnus station" for a day or two on the way home from an ISS crew rotation, getting them another world record and allowing them to run some tests. The PR value alone would be huge.