(Thanks to @Razzle1337 for the new info)
The Final Waves of Ranger Keys are coming soon, most completing each of their Seasons. But for some of the sets there are more than 3 more keys to be released. I took a look at some of the prototypes and ad Keys we have seen and what is left. From there I take a small prediction about what keys will be in the new packs!
*Please Note that Lightspeed Rescue was left out of the new key packs
38313 In Space B
In Space has already seen a release of Red, Black and Blue which leaves only 3 Rangers. Pink, Yellow and Silver have all appeared in either prototypes or as inclusion in other sets, therefore it makes sense that these three would be included in a Ranger Key Pack.