As a general rule building a new human biology is hard. Even making tiny tweaks to our existing biochemistry, such as calorie restriction mimetics, is proving to be very challenging to do effectively and safely. Reverting to the known good youthful state on the other hand, is less complex. So I'd expect delivery of replacement stem cell populations to be a going concern long before adjustments that produce MRL-like or spiny-mouse-like regeneration in humans.
The feature of aging that proficient regeneration seems most likely to help with is the business of fibrosis (liver, kidney, heart, lungs), where regeneration runs awry into excessive scarring, and damage to organs like the heart that do not repair themselves. Equally, it might have to be controlled very carefully in organs where structure is important, which would limit any early application. Recent experiments with cell therapy in the heart in monkeys produced disruption of heartbeat because of the formation of biological pacemarkers outside the normal parameters, for example.