While I understand the sentiment and where you are coming from, it will create certain problems.
For one, every Kind of “locking” (be it Content-wise or even just cosmetics) will bring some backslash with it. For the events, the items are already time-locked.
For some armor recolours and other frames they are skill-locked. This leads usually to people not ready for the task joining games they shouldn’t. While you could say “Incentive!” it is usually they kind of player who will never be ready.
So, now you are suggesting time- AND skill-locked content. I have doubts that this will not lead to an amplification of the mentioned problem. People will flocking to Cataclysm games for the wrong reasons leading to a “less joyful” time for all of us.
Unless FS implements a solution to obtain ALL time-locked cosmetics at later points, this problem will persist. And even if they implement, it would still create troubles. At least they have means to reintroduce these frames now with the Emporium.
It is not an issue per se. It is just something you have to Keep in mind. Especially since a part of the Vermintide Forum community (mainly the Steam Forum) has a tendency to act rather immature and take every straw they get to blame the developers.
Let us take an extreme scenario (realistically it will not play out like this): For one normal Cataclysm player who can play the difficulty, three new players join for this week, every game. This will normally lead to every one of these games being failed. Leading to noone getting the frame at all and a lot of frustration. It is just not ideal because even the players generally interested in Cataclysm will get a bad impression of the mode as they are more likely to be paired with other new players in that week. Could also lead to the general Cataclysm players being aversed to public matches (although I dont see that one, most Cataclysm players in-game are very patience, usually rather nice even if not to talkative and tend to actually play as team in comparison to Legend).
Like I said, this is an unlikely scenario. But elements of it will show up if you do it like this. Especially since people have the tendency not to lock at the things they can get (Recruit to Legend Frame) but more at the things they “miss” (Cataclysm Frame) even it is completely meaningless and borderline ugly and they would never even use it.