So in terms of flyable aircraft and Vietnam, with DCS we have the Huey and the MiG-21Bis (a bad guy with upgrades post-Vietnam). With the Huey we can service both the slick and gunship roles but more aircraft would be better. After doing some digging this is what I have found on other Vietnam aircraft and DCS.

AH-1 HueyCobra:
This aircraft is a must have for our gunship guys. In late 2013/ early 2014 this aircraft was on Belsimtek's official projects list. Recently, it has been quietly taken off the list and Belsimtek says their current focus is consolidating their existing projects (Huey, Mil-8, Sabre and MiG-15). Hopefully, once Belsimtek finishes playing with the MiG-15 they will begin working on this one again. Further, we know that when it comes to helicopter, Belsimtek knows what they are doing.

F-4 Phantom:
Probably the most requested aircraft by the DCS community and would be great LZ CAS. Nobody is putting their hand up to do it. Not even VAEO Simulations with their fondness with long development roadmap lists:
http://forums.eagle.ru/showthread.php?t=133226
VAEO is currently claiming the big issue preventing an F-4 module is intellectual property, but one wonders how this is the case if more US modern aircraft (F-14A&B by Leatherneck Simulations and F/A-18C by ED) are getting the full DCS treatment.

A-1E Skyraider:
This one would be very useful for LZ CAS. Interestingly, a modder formerly of the FSX community is trying his hand at bringing his FSX A-1E Skyraider to DCS:
http://forums.eagle.ru/showthread.php?t=136984
It will be interesting to see how Starway goes. In the meantime we are using the P-51D as a substitute and will soon have the P-47D (which I believe would be a even better substitute).

CH-47 Chinook:
The other iconic transport helio of the Vietnam war. Currently, officially speaking, VAEO appears to have bagged it, as it is currently near the bottom of VAEO Simulations rather long list of 40 aircraft on its Development Roadmap:
http://forums.eagle.ru/showthread.php?t=127100
So who knows when we will get it and what quality it will be. None of VAEO products have impressed me yet but they are only just starting out, so we will see.

Light Bombers: A-6 Intruder and F-105 Thunderchief:
Both good Vietnam era aircraft but unfortunately nothing official has ever been said about them. Currently, they only appear on Wishlists and have the occasional forum topic devoted to them.

That's all I have found so far. Feel free to add to this if I have missed something.

(C/229) Andrei Dragovic wrote:one wonders how this is the case if more US modern aircraft (F-14A&B by Leatherneck Simulations and F/A-18C by ED) are getting the full DCS treatment.

Boeing are notoriously protective of anything relating to their IP, and the only way you get a license from what I understand is if you pay the big bucks, or they commission you to build something for them (a la ED F/A-18C)

(C/229) Andrei Dragovic wrote:So who knows when we will get it and what quality it will be. None of VAEO products have impressed me yet but they are only just starting out, so we will see.

Judging by the scuttlebutt about the internal goings on at VAEO (not public knowledge, and I'm not really at liberty to say anymore, but) don't hold your breath. I also am not that impressed by the management of the Hawk release. VAEO were also going to pickup the A-4 Skyhawk but also dropped that like a hot potato after their initial discussions with Boeing (who purchased McDonnell Douglas) about the cost to license it.

I wouldn't treat anything on the VAEO list as anything but a wishlist of things that they would like to do... One day...

(C/229) Andrei Dragovic wrote:Light Bombers: A-6 Intruder

That's on the Razbam list of Aircraft to bring over from FSX after the Mirage 2000 and the A-7E Corsair II, but it's a ways off-> See here