Does that mean that those "Future considerations" deals aren't allowed anymore ?
Future considerations can still be completed, but the considerations need to be provided to the League at the time of the trade and the future considerations cannot be an exchange of a player at a later date, or cash. (Players, cash, team expenses, dinners, equipment were all exchanged in the past, but the rules have tightened up now.)
A common modern future consideration, as an example, is an AHL transaction between the two teams' farm teams, to cover any deficit. As those players are not on NHL contract, they are only referenced in the Leagues register as "future considerations". A recent example is Edward Pasquale to Tampa Bay from Edmonton for "future considerations". The considerations were fulfilled when Syracuse (Tampa's AHL affiliate) sent AHL player Ty Loney and Nick Riopel to Bakersfield (Edmonton's AHL affiliate).
Handshake deals (deals in principle without paperwork filed) have been enforced by the league previously. See the Eric Lindros arbitration decision.
The argument from the Nordiques was that there was no actual trade with the Flyers just an agreement in principle and the paperwork was done on the Rangers trade. We all know how that worked out.
The Lindros trade was not enforced by the League, but by an independent arbitrator, as mentioned. The League in a sense put their hands up and said, "you guys figure it out" (hyperbole).
After the ruling was complete, the League (Gil Stein) then came out of the woodworks to clarify the rule that "all [future] trades needed to be confirmed with the league office by all involved parties before they would be considered consummated".
Nowadays there is a very complex system to formally file a trade that sticks. The modern NHL trade deadline is a good example of this system pushed to the limits.