In truth, no one knows if a year flow will ever happen until 6 years from now. In 6 years, we can all look back and learn whether or not a 6 year flow was a good guess or a bad guess. Either way, it's simply a guess.

If I was betting money on it, I'd wager that a 6 year flow won't happen. 6 years is based on a very optimistic set of scenarios. Any number of events could and likely will slow or stop the flow:

A pause in hiring at mainline
Scope relief at mainline
Economic recession
Bankruptcy
War
Another mainline merger
Automation
A merger among the wholly owned companies
Etc.

It may be risky to go to a low cost carrier, but it's equally as risky to wait patiently in line for one's turn to flow.

My advice: Do what you think is best for you and your family, and don't drink the Kool Aid.