In most cases, if the president has enough confidence in you to ask your opinion on an important matter, you should have enough confidence in yourself to follow-up with him. If he is like most company presidents, he is extremely busy with numerous matters crossing his desk, and that is the most likely explanation for the lack of information back from him.
At the same time, your next step also depends on your working relationship with him. If he is an open, communicative, and responsive leader, then your decision is simple. He is a solid leader who invited you into the process, and you can certainly ask him how things are progressing on the issue in question.
However, if he is more of a closed, authoritarian, or volatile leader, then you may want to think twice about approaching him. For that matter, you may also want to think twice about your long-term prospects in a company with this kind of individual at the helm.
You mentioned that other managers were also asked for their thoughts on the issue at hand, and it might be helpful for you to find out if they have heard back from him. The information they provide could be informative to you in many different ways.
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