For my two cents, I personally am dreading any re-make of the GN/GNX. GM will NOT be able to get it right (Think Pontiac GTO), or even remotely close. With the elimination of many of their brands, I don't think they are not going to put anything on the market that will devalue flagships of their remaining brands. I don't think it will come from the factory being able to keep up with the Vettes, (especially now they they can get what they are getting people to pay for them) and I don't think it will even keep up with the top Caddy coupes. I think it will be like someone else mentioned, something in between.
I think the Challenger, Mustang, and even the new Camaro 'throwback designs' (Okay so there's one for GM) did their nameplates justice. Resemblance to the older models in appearance and performance in comparison to their peers.
The spy photos I have seen so share no characteristics of anything I would consider 'Trademarks' of the GN appearance, and given the competition levels of its peers, I don't think it will stand out in any way on the track.
Now my pessimism aside, if I had a blank canvas for a remake, I would start off with a similar front face as the Gbody.. single piece black grill, elongated yellow running lights/ turn signals, quad square headlight assembly, obligatory bulge in the hood, two door coupes only, and horizontal tail lights. I know I am gonna get flak for this, but YES bring back the T tops (except maybe engineered a bit better).
While the Turbo 4banger does sound a bit insulting, it really isn't much different than the Turbo 6 vs v8 argument from the 80s. I mean they have Kias coming off the factory floor with 275hp with a Turbo 4 which is more HP than the 5.0s had during the GNs peak. (granted Kia is FWD and they are NOT getting that HP at the wheels). So if a twin turbo 4 let me keep up with a Mustang/Challenger off the showroom floor, I 'might' consider it if it had the signature turbo whine.
Since performance wise it would be VERY difficult to offer something that dominates against its peers, I would suggest getting to those numbers a different way. I dunno if that truly conveys what I am picturing, but I guess I would like to see something revolutionary on a new GN. Imagine getting a 440 HP car that gets like 35 MPG and 0-60 in 4.5 seconds, AND seat 5. Something along those lines that would AGAIN change the way performance cars were deigned.
I guess my point is when I think of the GN I think of the 'what they did' with 'what they had'. Taking caddy, that looks like a caddy, and offering a trim with a GN badge and a dumbed down performance package, probably with a lot of the technology reserved for Caddys striped out of it, I just don't think would work.