Word of mouth, but this info apparently originates from inside flight ops leadership (Q&A with LCAs). To summarize:

-The company currently does NOT plan on actually displacing (read training) 4500 pilots. It is merely just the first phase of a worst case scenario battle plan to have in their back pocket
-Displacement training cycles will start June 01 from the button up. As/if the recovery improves they will cancel displacements from the top down (or on the contrary, create additional displacements)
-There are four furlough plans: 0, 1000, 4000, 8000. Still way too early to determine which is most realistic
-4500 displacements absolutely does not mean 4500 furloughs
-Anyone who’s junior and has had training cancelled does not mean they will be furloughed. The company is just trying to maximize displacement training throughput and doesn’t care if there will be “not qualled” pilots on junior fleets, since there will be such a surplus. If they have to go to the sim anyway (QMV/QLOE/landings), they’d rather kick that can down the road and re-qual them when they become needed and use the current sim slots in the near-term for Qualification courses as a result of displacements. A requal would just be a warmup, maneuvers validation, then line check.
-The current furlough breakeven estimate is 6 months based on the structure of the displacement (not 18 months as previously believed). While this may make it easier to justify furloughing X number of pilots, it is also that much earlier a pilot can expect to returning to the line should things really improve, IF a furlough even happens