Well the NHL already has endless movement, mostly in the form of "rentals" for Cup runs. That's one that irritates me, luckily those rentals rarely get to hoist the Cup.
At least under the last CBA these "rentals" were mostly veterans who were somewhat past their prime -- like Ray Bourque, for example. These were players who were 31 or older who would be unrestricted free agents at the end of a season, and they were traded because their team did not plan to re-sign them.
Look how awful the NFL system has become . . . contracts in the NFL don't mean anything because players can be cut at any time (imagine Michael Vick getting cut 90 days after signing a 10-year contract with the Falcons!), so you have all these "unrestricted free agents" out there who are no more than 24 years old and just entering the prime years of their careers.