Nikolaj Ehlers
A player of Nikolaj Ehlers's caliber would likely make the biggest impact starting next season, as he's a player who can slot in alongside Mat Barzal and Bo Horvat on the first line.
At 28 years old, Ehlers has one year remaining on his current contract with a cap hit of $6M - a price tag much more practicable than Marner.
Ehlers has scored 20+ goals seven times in nine NHL seasons, including those shortened by the COVID pandemic, with a career-high 29 in 2017-18. The only seasons he's been held under 20 goals were his rookie campaign in 2015-16 and the 2022-23 season, where he was held to 12, only playing in 45 games.
This past season Ehlers finished with 25 goals and 36 assists for 61 points - the second highest total of his career. He also finished with the highest Corsi-For percentage on the team outside of Tyler Toffoli, who only played 18 games for the Jets, at 54.68%.
Ehlers is a player who plays with speed and would have no problem keeping up with the pace of play alongside Barzal. Acquiring him would finally give the Islanders a three-headed monster on the top line that they've been without for a long time.
The biggest concern with Ehlers is his injury history. Despite playing 82 games last season, Ehlers missed 57 games in the two seasons prior.
Like the Islanders, the Jets haven't advanced past the first round of the playoffs in the last three seasons. They'll also likely be looking to shake up their roster, possibly making Ehlers expendable. Ehlers does have a modified 10-team no-trade list, but it's hard to imagine the Islanders would be one of those teams.