I think there are 2 different trains of thought going on here; One being teams using players on LTIR to circumvent the salary cap, and the other being once playoffs start, the salary cap goes away and players coming off of IR are able to slot into the team without the team needing to drop/waive players to make space.
The first part, teams using LTIR to gain cap space is nothing new, this will never go away.
Players being stashed on IR for a season only to be activated once playoffs start; Other than Kucherov this season, the only other extreme example of this I believe is when Toews with Chicago came off IR during playoffs and helped them win. This is a very rare instance for a player of Kucherov's caliber being on LTIR for the whole season. Once Tampa knew they were locked into a playoff spot, there would be no incentive to take him off LTIR earlier. If Tampa wins the cup this year, maybe, MAYBE, there may be 4-5 owners who say that a system needs to be in place to prevent this kind of 'Advantage' from happening again... but if it only happens once every 10 years, then really, the league won't do anything.
How about this for an example; Eichel decides to get surgery now, and is out for 'most' of next season. A team like Carolina goes and trades for him, just to have him sit on IR for the season knowing they are strong enough to make the playoffs without him. Once playoffs start, he is activated off IR, and help pushes the team to win a cup. Instances like THAT would likely cause GM's to make changes to the rules, but for now, I don't see anything wrong with it, nor do I see any rule changes being made because of it.