22nd January Update: I saw the latest Little Dev Update, it makes me feel excited, because I can define my own car colors as I want (Fun Fact: White still remained popular car color on last year, 2016, which looks bland in my personal opinion, so I want to have unorthodox body colors, such as Candy Apple Green, Sunrise Orange Metallic or Lightning Yellow Pearl available from factory). Anyway, both Tagora and Scorpio’s progresses are going well, despite the delay, due to some new assignments. After I finished all of the variants, I will talk to the dev to include my car.
I also have an important question: Can I export just the unskinned/unfinished models to test the car’s placement, like Rasyx’s yet-to-be finished Citroen Front 15 or Donkervoort in progress?
You need the skin, however you don’t need to define any of the morph zones. I just add the root bone and one other, then export. This skin is in essence “Disposable”
I find it’s good practice to do this and double check the placement and also for any other quirks like black polys due to overlapping vertices, etc.
4th February Update: Both Tagora and Scorpio are done, although the ongoing assignment made me finish those car late. I also complete remodeled the Scorpio just within 3 days (Friday, Saturday and Sunday) as a quick revamp. But this is not enough, I will create more variants before I send those cars to the Dev, such as Tagora Extended Wheelbase, Scorpio Sedan and Coupe.
When I’m converting it into a station wagon, I have an edge error on the 3ds Max.
Anyway, this is the wagon variant that I’m working on, and I’ll also made it available in the long wheelbase (similar to the Volvo 245T) as well.
Why it caused error in the above image? (Editable Mesh mode), however, when I converted to the Editable Poly, the problem above doesn’t occur.
10/2/2017 Update: I have both bad and good news for you: the bad news is the Thunderbolt was put on hold (not included as a part of UE4 update), because I want to revive the 1940s car project I examined during my early days of 3D modeling.
The good news is: I have now finished the Tagora variants, then I will follow by the Scorpio variants (sedan, coupe and maybe convertible, but the wagon is unlikely, because in some countries where liftback or hatchback and station wagon are both available, it may cannibalize the sales), after that, I will finalize the seams and separate the doors and trunk, and contact the dev to include my cars.
As I’ve recently learned myself, you don’t need to separate the doors and trunks from the body. That should save you some work. 
For the part of contacting the devs, they’re usually the ones to seek out the modders and ask about possibly having content included in the game. You’ve got potential, especially visible with your current WIPs, so keep at it and you very well might get a message from one of the devs sometime down the line regarding that.
I’d still recommend giving it a wagon variant as well. Even if some variants may seem unneccessary, it’s always best to give players as much choice as possible. The Scorpio body has potential for some great 80s executive cars.
Okay, I made a wagon variant as well, the Scorpio Wagon will be the sporty touring wagon. My Scorpio has potential because of the low-drag aerodynamic styling (available from 1978, because I want to make a highly-automated production cars, to make it look high-tech at both design and production. It may take 4 years to production stage as far as I tried, which will be likely to produce as early as 1982).
Here are the progresses, both cars progressed quite well, despite some delays due to the assignments/homeworks. However, both the morphing zones and hidden boxes are almost finalized as well (except the long Tagora variants, where I hadn’t updated yet).
The Tagora will be available in sedan (standard and stretched), wagon (standard and stretched), van (standard and stretched) coupe (standard only) and convertible (standard only), while the Scorpio will be available in liftback/hatchback, sedan, coupe, convertible and wagon.
Good News: I have now basically finished the base modeling of both cars, however, I haven’t edited boxes (Tagora Long variants), unwrapped and skinned yet, but I will contact the Dev to include my cars as a part of the UE4 update.
However, I have a small bad news: the Skyline 4-door convertible I did, will not included, because it unnecessary, due to the sporty nature of the car.
Well, who does need a 4-door cabrio Skyline anyway?
But I have a tip: Be patient when asking. Devs can eventually get angry if you’ll be begging too much (however this NSX looks delicious).
Who doesn’t need a 4 door cabrio Skyline? Get your priorities straight, mate 
No reason to not include it. The more variants, the better.
Okay. I want stretched 6-door widebody mid engined landaulet shooting brake Skyline.
I wouldn’t worry about that. I consider any body to be a blank page for the players to work with. The Pinto body can be used to make an awesome sports car, and the Skyline body can be used to make the blandest early 90s mid size FF grocery getter.
Anyway, I had decided to update my Skyline 4-door convertible into a Town Landaulet hybrid instead of canceling this variant, because there are no Town Car (Sedanca de Ville, not a Lincoln car) body style yet .
@Oskiinus lololol, Your idea is very creative.
@partario Sure, my car is very flexible, it can be from the conventional family car to the 1000+ hp ultimate tuner, like your Pinto can also be used from the conventional subcompact car to the high-displacement drag racer or sporty car as well.
o kurwa sunroofed landaulet
Ohm, but speaking of; Now I see that Skyline would make a great targa too xD
10th March Update: I have finished all of my mid-term tests, so I can now continue my modeling.
Although I have a bad news: all of my current projects will be on hiatus (but not cancelled) until the game updated to the UE4 (because I may also have upcoming assignments as well), although experimental modeling continues (I want to make the classic cars I desired, because the 40s to mid-70s cars are particularly under-invested (many gaps).
Despite my projects are on hiatus, you can still suggest/recommend those classic cars with some images as an impression before experiment (not a part of current project).
4/9/2017 Update: Today is the 1st anniversary on this topic. However, I have a bad news: all of my projects, except NSX and R32, will be cancelled due to the UE4 revamp changes, and even worse, my current topic may be deleted to separate into 2 topics (mods and suggestions) after the UE4 update. Anyway, I did some classic and 2010s car modeling practice to find some possibilities as well, and may replace those 80s cars.