Oasis and Augur both already use this technique for their order books. The client provides “hints” that tell the contract where to start walking from, and if no hints are provided it starts walking from head. Ideally, the contract supports arrays of hints where the first hint that still exists is used. This is because in a high velocity order book it is possible that in the time between when the transaction was crafted/signed and the transaction was mined the hinted item may have been deleted. By providing multiple hints you reduce the chances of having the hint miss.
The reason for having the contract walk from the hint is because in the time between transaction construction and mining new items may have been inserted into the list such that the previous hint, while close, is no longer the exactly correct insertion point. This results in O(n) walking, but if the hint is “generally close” n is small.