Naismith, 24, had 18 months left on his original deal but has been secured long-term after signing a contract extension that keeps him at Ibrox until May 2015. However, a question mark remains over whether Miller will still be a Rangers player beyond this season when his contract is set to expire.
The striker, celebrating his 31st birthday today, has been in fine form this season and has already netted 20 goals.
So far, contract talks have failed to yield an agreement and Miller has been linked with a return south of the border, but McCoist has refused to give up hope of retaining his services.
He said: "We would all be delighted if he stayed. I know his representative and (chief executive] Martin Bain have had lengthy discussions.
"It's not over the line yet but we are very, very hopeful that Kenny will be staying here and signing a new contract. You have a word here and there but it's only fair to let Kenny make his own mind up. He's got a young family and decisions to make and it will be his decision only but hopefully he stays."
McCoist welcomed the news of Naismith's new deal. He said: "I'm absolutely thrilled. Steven has come on in leaps and bounds this season."