As a Flyers fan, I'd love for this to happen. However, I don't think this will happen for Philly if Poile wants to sell prior to the expansion, and here's why...
Assuming they get Ekholm, that'll give them Provorov, Sanheim, Myers, Ekholm as your top 4 (NICE). However, expansion draft is coming and that means you're losing one of those, and odds are it'd be one of the young guys.
If NSH would wait til the offseason, after the expansion, I'd be inclined to throw in either a 1st, a good prospect like Frost, plus an NHL-ready player with a low cap hit (i.e. Hagg).

I'm not super up to date with this news though so idek if that is what NSH is looking for.

A 1st, Frost and Hagg imo

I think it would be something similar to the Muzzin deal do a first and 2 B prospects who those prospect are I'm not sure maybe something like Ratcliffe, Andre, and a first or a instead of a prospect a roster player like Hagg to replace Andrea. I'm also viewing this as a rental deal for the flyers where Ekholm is left unprotected and probably taken.

I wouldn't give more than two 2nds for this rental.

There is an Athletic story that compares Elkholm's contract term/length to Muzzin and Martinez. Muzzin netted the 1st + 2 prospects. Martinez netted two 2nds. Both teams figured they were getting their d-man for the full remaining length of the contract, basically 1.5 seasons. Elkholm will be likely be exposed and taken in the expansion draft, which means 0.5 seasons instead (rental).
I don't see the Flyers exposing any of their three under-25 d-men, and they shouldn't pay Seattle anything more to not take Elkholm since the total cost for the player would be too high.