Bratt + Severson + 1st + 2nd?
Value wise it's fine, it's just that we're competing for a playoff spot and trading Bratt would create an enormous hole on our right side; outside of Palmieri & Bratt all we have is a bunch of washed up trash like Hayes & Stafford.
Realistically the only non-futures piece we can send back is Severson, Karlsson would be taking his spot anyway and i'm sure he'd be an attractive piece for Ottawa since he's a young cost-controlled (with term) replacement for EK. Other than that I doubt we'd be looking to considerably weaken our existing roster to accommodate a trade like this, absolutely nothing is off-limits pick-wise or in our prospect pool (i'd give up a wealth of futures to get it done) but I don't think there's enough value in upgrading Severson to Karlsson to justify losing Bratt.
To clarify, Karlsson is undeniably MUCH better than Severson, but losing Bratt means two of Stafford/Hayes/Lappin (AHL plugs) being in the lineup on a nightly basis, that kind of a setback wouldn't make sense of us right now when we're chasing a playoff spot.