In my opinion, managing traceability is difficult especially if the product is very complex in architecture.
Though it is tough, I do not perceive it as impossible.
The only place this falls through the cracks is when the product starts to grow and people do not have time to maintain or reuse it efficiently and effectively.
One of the easiest ways to maintain it for the benefit of all groups in SDLC is to maintain it centrally. Have a few people team working very closely with architects who track each and every impact.
The methods to track can be either through something as simple as an xls or through various tools available in the market. BPM and BPT(Business Process Modeling and testing) can be one option.
A small tracker will need to be maintained further as a subset of traceability tracker to know proper coverage of: Positive tests, Negative Tests, Performance/Load/Stress, usability... etc ..etc based on your needs.