Their goaltending hasn't been very impressive in recent post-seasons. I'm not one to let their forwards off the hook when their offense dries up in the 2nd and 3rd rounds, but they could absolutely use a gamer like Binner.
Kochetkov is a good goalie and someone the Canes are hoping is their goalie of the future. I highly doubt they're interested in blocking him long-term with Binnington and his contract. I certainly don't think they'd trade Necas and thin themselves out at forward to do so. Freddy Anderson is a solid goalie too so it's not like they're thin at the position when healthy.
I love Binnington, but what he did in the playoffs on the run to the Cup was almost a half decade ago and last season aside, he hasn't performed at the level of someone who you would think a playoff team is going to give up a premium asset like Necas to add.
I've said it before and I'll say it again, if the Blues were in a playoff series today, I'd feel great with Binnington as our starting goaltender. I just don't think people around the league put him on the same pedestal.