ISM planned the all dragon coins TAS originally in SMW, but a few problems made him quit this project. He pointed them out in
his blog; the summary is like this:
a) The existence of dragon coin glitch. This is so serious because it would enable us to get yoshi wings in almost all the levels, and to collect dragon coins in the sky levels.
b) The game can't save the collected dragon coins, as Zowayix pointed out above.
These problems make it difficult to understand the "all dragon coins" goal. Possible goals are maybe:
1) To collect all possible dragon coins including those in the sky level;
2) To collect at least five dragon coins in each level which possesses dragon coins.
The first one is impossible, because we can get a yoshi wing in VS2 but we don't have time long enough to pull it off. The second is also impossible since, for example, SW3 has no dragon coins in the usual level, but 4 dragon coins in the sky level. The other goals may be so arbitrary.
The problems are all solved in SMA2. That's why ISM made his SMA2 run.
EDIT: you can get his test movies on yoshi wings, in
this entry.