My Little Pony/WMG

Humans are the source of all evil!
Or, more specifically, humans are the source of the "villainous" entities in the Ponyverse. The Talesverse lacks both humans and the frequent assaults of said villainous entities. As both continuities are set in an explicitly magical universe, it could be argued that humans somehow subconsciously generate the evils when in an area with magic. In fact, one could conceivably do some Arc Welding and say that at some point between the two series, humans were barred from ponyland specifically because of this trait....
 * Actually, compound that: Some humans (mostly female) did not want to leave. So, they consented to being turned into ponies themselves! Morphic Resonance allowed them to manipulate objects with their forehoofs...
 * ...and maybe, if we allow for a few generation's difference, the Talesverse could eventually morph into Friendship is Magic! Okay, yeah, I'm just trying to unify the whole series, sue me.
 * That's plausible, after all Ponyville was founded by Earth Ponies, and everypony in My Little Pony Tales is an Earth Pony.

Generation 3 ended when the ponies fell under a reverse-aging spell they couldn't cure.
The first sign was Rainbow Dash's voice getting higher. Then every pony got smaller. Then they were babies. Sure, the ponies may claim they were "remembering" what they did at that age, but why is the same gang of seven all together in the baby series when that group of friends didn't form until the later G3 videos? They're really just describing the deja vu they experience as they try to deny the fact that they're about to shrink away to nothing.

G3.5 is AU or non-canon from G3
There are far too many continuity errors.

G3 ponies are magnetic, that's why they can use Invisible Anatomy
The toys have magnetic hooves so why not? For the things they hold that aren't magnetic.. Then maybe it's magic, or everything is magnetic in the Ponyverse?

G5 will be even better than G4
Because they'll know what they did right in G4.

G5 will recieve tons of hate from butthurt bronies regardless of its quality
Pretty self-explanatory. In fact, I'm sure this definitely will happen to some extent.

Glory and Moondancer are married
They did have a porcelain called "Wedding Prance" where they appeared to be getting married.

G3 is set after g4
It makes perfect sense: the two alicorn sisters went with the wild whipper. All the ponies with similar names are decendance of the mane six