The Flash/WMG

The Speed Force and the Metagene are related to Magic: The Gathering's Planeswalker Spark.
See Magic the Gathering for details.

The speedsters created the Speed Force, not the other way around.
Those with the proper Metagenes pooled their powers into a single extradimensional space, causing it to become increasingly sentient and influential. Their speed comes from themselves and flows into the Speed Force. The original energy comes from the same source as all the other energy-generating metahumans. Possibly The Source is the source.
 * Confirmed by Rebirth #4! And people are already throwing hissy fits!

Alternatively both the speedsters powers created the Speed Force just as simultaneously the Speed Force gave them their own powers
Given that the Speed Force permits Time Travel, this would be a Stable Time Loop.
 * Effectively confirmed. Barry created and is the source of the Speed Force.

That place Mirror Master goes when he jumps through a mirror is Despair's realm from The Sandman.
Despair's realm is "The World Behind the Mirrors". How could it not be the same place? As to why they've never met -- notice how we never see the bottom of it in the Flash comics. Despair always hangs around on the floor.
 * Who says they've never met? Maybe Mc Culloch was terrified into silence by the experience, or maybe he thought it was a cocaine-induced hallucination.
 * Who says that he was silent about it? Maybe he does tell people, we just never see it on panel.
 * Actually, this fits pretty well. Both men started using the mirrors after experiencing great despair: Scudder had recently began a 10 year prison sentence for robbery and Mc Culloch found out he had shot his biological father and driven his mother to suicide.

All speedsters in every universe gain their power from the Speed Force
Flash, Quicksilver, Sonic the Hedgehog, Synapse, Superman, even the fastest Transformers and race car drivers gain their affinity with speed from it.

Alternately, the above theory that speedsters create the Speed Force could also be true in this way.


 * Corollary: All motion in all universes comes from the Speed Force. All motion is relative; To a snail, a turtle has super-speed. Basically, the Speed Force is just the multiversal clearinghouse for kinetic energy.
 * I'm new to the Flash, but in Rebirth it implies the Savitars got their speed by sacrificing people? If they had any connection to the Speed Force other than Savitar being imprisoned within it it forcible then this could be evidence for this WMG.
 * I seem to recall reading somewhere that Superman's speed is simply part of his genetic makeup from the powers he derives from yellow solar energy, and thus is not connected to the Speed Force in any way. Plus, Jay Garrick is a speedster, but didn't lose his speed when the Speed Force temporarily disappeared due to his powers coming from his meta-gene.
 * Jay Garrick is the prime example of not all "speed" feats being from the Speed Force. In Rebirth he states he was never able to run faster than sound on his own. He met Barry and then he could run "faster". The implication being was that he was now hooking into the Speed Force.

The Darker and Edgier story about Barry's parents is, in canon, a continuity burp.
Consider these following points:
 * 1) Barry instinctively believes that his father is innocent of the crime of killing his mother.
 * 2) Geoff Johns is the man who came up with the "Superboy-Prime punch" explanation for hiccups in continuity.
 * Geoff Johns didn't come up with the "Superboy-Prime Punch" that was Judd Winick.
 * 1) Geoff Johns is also the man who created Hunter Zolomon, a.k.a. Zoom, whose father was a serial killer and killed his mother.
 * 2) Johns loves the hell out of Zoom; even though he depowered him in Rogues' Revenge, he's not about to give up his favorite Flash villain so easily.

Ergo, there's been some weird reality shifting that has caused Zolomon's history to be ascribed to Barry, and Barry's going to need to figure out how to fix it.


 * It's a different kind of continuity hiccup. Barry died just before the final reset in the first Crisis. Since then, there as a Crisis In Time which altered backstories, Infinite Crisis, which resurrected the Multiverse and, again, altered parts of history (kind of like 52). Look how much Batman and Superman have changed since COIE; the only reason we didn't notice any changes in Barry before was that his personal timeline had ended mid-Crisis before.
 * Not mutually exclusive...


 * Turns out it was the original Professor Zoom retconning Barry's past.

The new Barry Allen will be a villain
This follows naturally from the above guess. We've got two other Flashes for heroics, so...

Flash can fly.
Theoretically, there no reason he can't; he can violate every other law of motion, inertia, and gravity at will. Johnny and Jesse Quick, who also tap the Speed Force, can fly. DC's version of Mercury/Hermes, God of Speed, can also fly, and those who gain "the speed of Mercury" such as Wonder Woman and Captain Marvel also gain flight. The Kingdom Come Future!Flash can fly.
 * It's been implied that Flash can fly by propelling his molecules in a fashion similar to flight. He doesn't because: A) There are all ready several fliers, and several speedster fliers; and B) He's got the whole running thing down to a science, why both with flying?
 * The meta reason is it gets boring if everyone can fly. The in-universe reason seems to be that it would practice to do it and failure will lead to... eh.

Parallax is now able to tap into the Speed Force.
At one point in Brightest Day, Parallax was able to combine Barry Allen's speedster powers with his own Reality Warper fear-mongering abilities through possession. Once a speedster touches the Speed Force, (at least presumably) they can tap into it again. Thus, Parallax, via his short stint with the Flash, has acquired superspeed.
 * Why does it matter? Parallax is the personification of fear, the cause of it, and presumably is fear. That probably qualifies it for being everywhere, to some extent, where there is fear. If you can be in so many places at once, why would superspeed matter?
 * If that is the case, then fear is now capable of striking anywhere, at any time, in the blink of an eye, when it could only come in leaps and bounds before.

In another universe Jay Garrick is FLASH! AHH!AHH!...
and Hawkman is one of the hawk people. Queen.

Wally is still Kid Flash
to Jay Garrick on Earth-2.