@OIM20
Answers:
1) Is it realistic? It may be unrealistic for the developers to "devalue" their MA artifact table, but this isn't really what would occur except on a limited time scale. There may be a period of time that the offers to craft artifacts are less accepted, but in the long run the excess artifact inventory would shrink and the actual perceived value of the artifacts return to the price asked. Right now the excess inventory is an unusable resource. Once that resource is used up, it's gone and the asked for price will be the price accepted if the player determines it's worth it.
In addition, is the use of a wide ranging 2:1 ratio of exchange anything more than what has twice been done in the MA? -- though for specific exchanges, of course. The ratio has twice been 2:1 and only the duration and ranges of the offer would change. Since it's been done, short term, the only issue is making it, more or less, permanent and building a rotation of offers. One week two of these for one of those, sort of thing. This would "draw down" the amount of artifact inventory, and give the players a sense that they artifacts they earn/win have some value (they have none in inventory if they are for evolving buildings already built and at maximum evolution). This would help a lot of mid-range players who might be short one or two artifacts they need because they were unable to earn the full compliment needed during the event and the FA afterward. In essence they could substitute the "extras" or ones they didn't intend to use, for what they were short.
2) Do the developers see this as a problem? I doubt they see it as much of a problem for the reasons you offer. However, game play is not about what the developers see as a problem, but what needlessly hinders or undermines the value of the time and effort the players put into the game. If you can make the game more enjoyable without drastically changing it's game play, and you can do it fairly easily, it should be done for the "bottom line."
I can't answer to how it might work in the trader, but mechanics for the MA are already in place and all that needs to be done is make a rotation of offers -- just as they do in the Spire for artifacts. The OP seemed to have this in mind in his/her post as well.
3) While it is possible to add this to the Spire, via Soggy's good suggestion, it would be easier to parallel the method used in offering artifacts in the Spire, as noted immediately above. Easier, faster, and just as effective in solving the excess artifact inventory problem many of us perceive to be a problem.
4) Predicting real world responses to change is a matter of looking at who benefits and who looses. In this case a lot of mid to upper level players who have accumulated a bunch of, now worthless, artifacts, would benefit. Lower level players, not so much, but how would they be harmed? Maybe they would be offered only the offers for the excesses they actually have? I they have 2 cold phoenix artifacts in their inventory they might be able to trade them for 1 bear, for instance. If they don't then the offer isn't made. Here I'm thinking of the MA offer rather than the Spire idea.
In the end I do see some downsides to the idea, but not enough to think it a bad idea. And I do think the alternative proposed by Soggy would take a lot more programming and, since it seems to be offered as a solution to largely the same problem, perhaps cheaper and easier to implement is better?
Finally, I appreciate, very much, your measured and careful analysis and discussion of this matter. As one who, too often, "shoots from the hip" you remind me to be more careful and think a bit more before I respond. Thanks.!
AJ