They have a steady pattern. 2 waves a year. (3 & 4 we're one wave) for release around the end of quarter 2 and around the end of quarter 4.
As for the Squadrons, there may be a pattern there as well. Stats below are totals of ship types and squadron types.
Wave 1- 5 ships, 8 squadrons
Wave 2- 9 ships, 16 squadrons
Wave 3- 11 ships, 16 squadrons
Wave 4- 13 ships, 16 squadrons
Wave 5- 15 ships, 24 squadrons (SWM20 concept created possibly 16 ships from FFG's perspective)
Wave 6- 17 ships, 24 squadrons
Note: Ship count is never allowed to exceed squadron count.
Assuming 2 ships per wave is the new normal, we have until wave 9 or 10 before the next batch of squadrons show up, or 6-8 more ships if you are hoping for more than 2 ships per wave.
Wave 7, I expect to see only 2, mostly because the SSD will be released at about the same time.