(1) IF there is a working formular, would the proposed system be desireable?
and
(2) Is it somehow possible to find such a formula?
I guess you already pretty much answered this way in your post, but I think it is worth repeating.
(1) Perhaps so... From the "reality" point of view (and most of us probably consider that to some degree about most everything in this game), it would seem weird and wrong. From the game-design point of view, it might work all right. The buying
decision is about improving your team. The selling
price is currently somewhat up to luck. Both are affected by the market, but not always to same extent (we all know the complaints about time of auction deadlines etc.)
(2) Considering that implementing the formula would remove much of incentive for overpaying (current TPE considers also overpriced transfers), once the change is in place the market data would certainly be better than what we have today for TPE.