In the case of Gundam NT and Fate/Stay Night those two movies were released directly by the companies that made them, which is why they were released so fast in the US. In the case of Gundam NT, Bandai Visual commissioned the dub themselves and it was released on Blu-Ray as an import, no US based distributor has the license to it (making it difficult to find it for a reasonable price on Blu-Ray).
RightStuf is the official distributor for all things Gundam and it WILL eventually get a commercial release since the did the same thing with both Unicorn and The Origin where they released and import version before they later on released an affordable collection. Give it time.
If there is announcement for Stampede (as well as more episodes for the main series) it will likely be in October to coincide with the 20th anniversary. Which maybe part Toei's doing, since Funimation is hyping the 20th anniversary on their site, as well as Toei's history of being more hands on with their properties when dealing with foreign distributors.
It will be great IF that happens then, all I'm saying instead of putting my expectations into milestones lets just see what happens when 2020 roles around. They ran out of TV Specials, Stampede would have to be announced and this is the point where something has to give.