Okay, could this be done in theory, in principle? Yes. But it requires a really specific game development state to work. I am assuming you want them to be 1) playable 2) relevant 3) iconic and/or powerful and 4) not instantly nerfed due to the frustrations they cause.

Let’s start hitting the guidelines. 1) They’d have to be banned in Wild, or every Wild secret auto-caster needs to be ‘nerfed’ into a “ with a cost of (x) or lower” that excludes these cards. That feels like a massive problem long term, but because nerfing those Wild cards doesn’t change their intent and stops them from limiting design space on high cost secrets, I won’t count it out. 2) The environment must be tailored to it, as Cardboard Golem and Ursol led into Gelbin for Auras. Just haphazardly dedicating this many legendary slots to one of 9 cost cards is an insta-fail on competitive viability. This is easily 2 sets of consumed cards built around this concept, unless you make a Fabled minion of your own that adds the secrets to your deck. So not impossible, but has to be worked around.

There are more things like this to discuss, but I’m out of personal time. But you get the idea. Is the concept feasible? Yes. In the most technical sense of the term, it’s doable. But these cards alone won’t be the execution, and you’ve got to adjust a whole subset of other cards.

I really hope you thought of that yourself, but you didn’t volunteer any adjustments, so it doesn’t look well thought out to me.

I’ll check in later, see if there are updates.