A completely peer reviewed editing system doesn't exist in the way you want, and suggested edits are not the way to add the functionality. You are looking for a way to propose a modification to an existing answer and have the the author or several people who are experts in the topic (or at least well versed) look at it and say "Yes, that is an improvement".
It sounds great, but I think you are grossly overvaluing the quality of the review system. In most cases, the reviewer is not going to be well-versed enough in the subject matter to make a judgement (and in many cases, they will have no clue). Likewise, suggested edits that change the answer are often discouraged (partially for this very reason).
So in the end you are going to have 1 of 3 things happen
- The edit will be approved by people who have no clue, and as such the peer review you were hoping for did not happen.
- The reviewers are going to see an edit that changes the answer or adds new information, and will reject it (usually as an "Invalid Edit")
- You get extremely lucky and happen to get 3 reviewers who know the subject matter or the original author and say "Yes that is better" and approve the edit.
Bullet 3 will be rare since there suggested edit queue moves so fast (at least on Stack Overflow). Edits are reviewed on a first come first serve, so there it would be extremely rare to get the OP or 3 such reviewers who happen to be in the queue at the same time as you propose your edit and they all happen to be shown your edit. So in the end, you are either going to get your edit approved by 3 people who didn't really evaluate the quality your changes like you want or it is going to get rejected.
The appropriate way to handle this is to comment on the post and let the author of the answer know what you think might be a better way. And then let the author make the judgement himself and whether to edit it in or not. Or they might make a comment back to say it is good, and let you edit it in.
The other option is to write your own answer. Obviously this depends on how different your "non-trivial" change is and how it would change the answer. If your code is indeed better, then maybe it deserves to be its own answer.