The truth is, last season Eberle didn't make much sense for the Isles. We had an excess of non-physical wingers in Okposo, Nielsen, Strome, Nelson, Prince, etc. However, Ladd is much more physical/defensive than Okposo, and with the physical Cizikas and Clutterbuck likely to see bigger minutes (joined by Chimera), the Isles offensively look much more physical then the were last year. And we still need more RHS forwards, as Strome, PAP and Clutterbuck I believe are our only ones.
So yes, Eberle does make sense. And I'll say I think he would be brought in to play second line minutes away from JT (especially since PAP is clearly slotted for his RW) and hopefully add scoring depth, something this team desperately lacks. Boychuk+ for Eberle would absolutely be ideal for the Islanders. Pulock takes Boychuk's spot on the 2nd pair and Mayfield takes Pulock's spot on the 3rd.
As for what the + would be, I'm not sure. It could go like the Hall-Larsson trade and be no + as the GMs recognize the significance of RHD to Edmonton. From a value standpoint though, I'd say it'd be something like a 2nd.