Before I start, I'm sorry if you find my English poor, it's not my first language, I was using Google Translate in most cases.
TL;DR at the bottom.
You called this new system as "Nightwave" and gave it the theme of radio-broadcasting, or a TV show, or theater. It includes such terms as "Act" ("Episode") and "Intermission", as well as theaters do.
In theaters, the first act introduces the viewer to the events. In the case of Warframe, as I understand it, players are both actors and spectators. They perform certain actions and progress in "performance", receiving rewards.
In theaters, when the performance is over, an Intermission begins. This is a pause between acts. Usually, during intermission, viewers can purchase souvenirs related to the past episode.
In the case of Warframe, there is a Nightwave store, where, in fact, these "souvenirs" are sold for spectators (players)...
What am I leading to. When the "Intermission II" began, as you may have noticed, many players began to complain about the presence of already received rewards at Nightwave ranks. In addition to this, new, or important (consumable, such as Forma Umbra) rewards are placed after the returned ones. Thus, in order to achieve new rewards, players must go through already received ones and, therefore, not receive anything for their efforts to achieve a certain rank.
I have a few suggestions on how to change the system before it's too late. "Too late" in this case is when some player reaches a rank with a problem reward. At the moment of posting this, the maximum rank is 3 + 9,500 Nightwave standing. So, the first problem reward (returned one) is at rank 8:
8. Wolf Salute - Emote
Suggestion No. 1:
For players who have already received recurring rewards, replace them with Intermission II Creds. Thus, that rank will not be "empty" for these players.
Suggestion No. 2:
Move all returned rewards to the very end. The total number of such rewards (related to Nightwave) is 7. Or 8, if you take into account the Liset skin. Then the rewards for ranks from 23 to 30 would be:
23. Wolf Salute - Emote
24. Napalm Grenades (Augment)
25. Eidolon Ephemera
26. Ancient Scrawl
27. Liset Athari Skin
28. Wild Frenzy (Augment)
29. Saturn Six Syandana
30. Saturn Six Armor Bundle.
Thus, players who have already managed to get them will not be demotivated during reaching max rank (if they feel like it), and players who have not had the opportunity to get them will try better, because this is the "second chance", which traditionally requires more effort.
Suggestion No. 3:
If you want to adhere to the theme of the theater, then it would be logical to move all the "unique" (ranks) rewards of Intermission (current and future) to Nightwave store, as well as those which returned from previous Episodes. While as rank rewards, you leave only items that are available outside the Nightwave (slots, Endo, Kuva, etc.) and Intermission Creds. And leave these "unique" rewards for achieving ranks only during the main Acts (Episodes).
That's the purpose of the "Intermission", when:
no action takes place (in theater), therefore, players should not get anything "special" for completing tasks and achieving ranks, because everyone is on a break from the Main Acts;
"souvenirs" related to the main performance can be purchased at the store by those who need them.
The way everything looks right now is as you cater to those who were lazy, or away, or unexperienced, during the first appearance of event and punish those who worked their way through.
OR at the very least: Please, fix duplicate appearance of cosmetic items in arsenal/inventory, make them stack.
TL;DR: Nightwave is theater-themed; Returned rewards placement should be rethought by devs; Only Main Acts should have unique rank rewards; But they must return in future Intermissions into the store.
Thank you for your time.