I'm not sure if this is a question, per se. If the OP is asking if the current rules permit a trade in which player A moves from Team X to Team Y for the remainder of the regular season and playoffs, at which point the player reverts to Team X again, then the answer is that this is not permitted.
There are no timed components permitted to a trade like this. It is also highly illegal for teams to have an agreement in a drawer (e.g. Team X cannot officially move player A to Team Y, but with a second secret deal in a drawer in which they move the player back to Team X at season's end for a particular agreed return). If the league finds out about it, the fines and draft pick penalties would be severe. The league would also probably suspend front office officials found to be complicit.
To swing these sort of transaction(s), Team X needs to trade player A to Team Y today. That ends the transaction. Teams X and Y can certainly discuss a second unrelated trade that might follow in the offseason, but the key is that there is nothing binding about any of those discussions today. Any developments in the interim (e.g. the player earns a Conn Smythe Trophy between then and now) will impact the player's value, potential future destination, and the return. Neither team is bound to any previous musings about what might occur in future. Either team can decide it does not want to pursue this second trade and back out.
If the OP is well aware of this, and is instead suggesting that the league look at introducing the concept of rentals, then that's a different issue. I think the answer would be that there is no appetite for this, though. It is true that teams loan players to other teams all the time under FIFA, but I don't know that this is ever between teams in the same professional league. In hockey, the NHL has a hard cap which adds new layers that are not present in international soccer (Fair Play rules notwithstanding).
As something that would have the whiff of cap circumvention, I think the league would put the kibosh on proposals concerning such a rental arrangement between NHL teams. Such a proposal would get shot down quickly.