@Ea can you put S4 flatline skin in shop or new skin with same iron sights?

Respawn are free to sell recolors of battle pass skins as they see fit.  They've already done so with several legend skins.  Just several weeks ago they sold a recolor of a well-regarded lifeline skin from an early battle pass.  I don't expect them to do so with lvl 100 weapon skins, but who knows?  In S11 the ad copy for the battle pass was changed, and they can freely sell anything again that they want to from S11 onwards.

Edit for OP:  I don't think you can purchase it right now, but the Champion Edition comes with a Flatline skin (Slayer's Lancer) that has iron sights just about as good as those on Heat Sink.  You could probably purchase a digital code for the edition second hand, or wait until they figure out what they are going to do with the stuff from this edition going forward.

@PanerossWell my child since your not that clued up allow me to enlighten you. Alot of console players choose the heat sync ironsights over a sight. It makes the fov cleaner and the recoil feels easier. Most console players use a flatline for mid to close range. Especially in arena where round 1 you can only afford a groudloot flatline. Nobody said anything about loosing gunfights young padawan or my playstyle. Im talking about the ironsights being incredibly clean which in turn makes the gun feel much better to use theres a reason why its a sought after skin not because it looks cool. Because it does not. The ironsights helps even just a little but it does. Im sick of having to ask for it to be reskinned by someone when i should just be able to purchase it for myself. So kid think before you type as you made so many wrong assumptions right there.

@UncheerfuIlLol too bad you'll never get your way. You missed your chance to get it. And it will never be in the store. Theres never been a lvl 100 BP reward in the store and there never will be.