When will be the next realignment election?

[Virginiá]

If the GOP wins in 2024, Dems win the House back in 2026.

Do you mean win as in a 1994-style ousting, or simply taking back the House due the typical WH-incumbent-party-loses-seats-in-midterms?

If 1994, then it's worth noting that things were different back then. Ticket-splitting happened much more and the Southern realignment reached a tipping point where enough House seats were changing hands, in addition to gains elsewhere, to tip the chamber.

The current realignment is occurring mainly along generational and racial lines. Heavily Democratic Millennials are growing up, along with an exploding minority population which is on its way to being unanimously Democratic, means that the House could flip before 2026 or maybe even after. A large majority of Millennials currently vote Democratic regardless of who is president, so we don't need a Republican president to "push" them over.

[Virginiá]

Realignment elections are mostly a myth.

If you're saying that as meaning one or two elections create a realignment, then you're probably right. Most realignments tend to happen over time with noticeable changes in views or ideology of the general populace. Eventually a presidential election comes along where a candidate strikes a chord with the new majority and that generally begins, or even continues, the change in the power structure.

So in reality those big elections tend to be more a result of the realignment rather than the cause.

[Virginiá]

Could be this one. Especially if we see both parties fracture (which is quite likely)

Democrats are not even close to fracturing. A primary with a generation gap isn't as significant as one may think.

[Virginiá]

You do realize that the Democratic edge with 18-29 year-olds was literally cut in half between 2012 and 2016, right?  It seems that that generation is already moving back towards the center.  Let's see how the 18-29s vote in 2020 (I expect a single-digit margin).

What?

Obama '12:  60 - 37
Clinton '16:  55 - 36

That's not half. Hillary lost 5 points and Trump actually did a point worse than Romney. That's not moving back to the center. I'd venture a guess her drop in support was mostly due to Hillary being Hillary - Millennial disdain for her was bound to cost her something. Also worth noting here is that Hillary did even better (and Trump worse) with 18-24 year olds, 56 - 34. That's fking terrible for the GOP.