I'll add a caveat to the #1 need being an edge rusher.
Saleh needs an ER but he needs one he can trust just as effectively against the run.
Right now, he has Watson who earlier in the year, showed he was a slightly better SAM ER over Harold. He also has Dumervil who seems to have plenty in the tank and Marsh, who's added a non-stop motor at LEO.
But in the end, he's using his heavier packages and better run defenders in Harold and Thomas more on early downs: first 2 downs before using his nickel (Thomas at NT, Dumervil at SAM and Marsh at LEO)
Saleh will need an Aldon Smith that he fully trusts to play on every down. Just like he'd like balance for Thomas to play the run inside more, he'd like to find that same trust in a SAM and LEO who could play almost every down without losing anything in the run defense.
Teams pass so much on first and second downs now, having edge rushers who can be just as effective against the run is critical for helping that back end and in collapsing the pocket to pair with the interior rush we have.
I'm "assuming" Saleh would like this but maybe not.
Technically, he could be rotating both Dumervil and Marsh at LEO every down but my guess is, he feels he'd lose in run support on the edges so he goes with a better run defender in Thomas (and Armstead before him) on the first two downs.
[ Edited by NCommand on Dec 18, 2017 at 3:43 PM ]