1.3: WHAT WOULD EXVEEMON, ANKYLOMON AND AQUILAMON DIGIVOLVE INTO IF THEY DIDN'T DNA DIGIVOLVE? WHAT ABOUT STINGMON?
The most commonly held belief is that they would still become Paildramon, Shakkoumon and Silphymon.
In the anime, Stingmon, Gatomon and Angemon act as an additional power source, giving the other Digimon the power to reach it's own natural Ultimate level. In season one, the Crests provided the additional power, but in season two, there were no Crests to do this, so the other Digimon were used.
There is, of course, no special reason that Stingmon could not have used the Crest of Kindness to Digivolve on his own, beyond the fact that the writers did not want to use this idea, and maybe because Ken might have needed a Tag. Had he done this - or had he used ExVeemon as a power source - he would have become his own Ultimate, DinoBeemon.
In one of the Digimon handheld Japanese games, you can DNA Digivolve ExVeemon and Stingmon into either Paildramon or DinoBeemon - and you can also DNA Digivolve Ankylomon and Angemon into either Shakkoumon OR MagnaAngemon, and can also DNA Digivolve Aquilamon and Gatomon into either Silphymon OR Angewomon - and MagnaAngemon and Angewomon, as everyone knows, are Angemon and Gatomon's natural Ultimates.
And to be blunt, no other Ultimate forms were ever designed for these three Digimon, as they were never going to do anything BUT DNA Digivolve. The D-Terminal states that ExVeemon becomes Paildramon, Stingmon becomes DinoBeemon, Aquilamon becomes Silphymon and Ankylomon becomes Shakkoumon - therefore the lines have been officially appointed by Bandai, and if you don't like it, it doesn't really matter.
As to Megas - Paildramon's is still Imperialdramon, while Shakkoumon's is Vikemon, and Silphymon's is Valkyrimon. DinoBeemon's is GranKuwagamon.