A. The traditional asset allocation is a L-shape in terms of stock exposure as you age, however, a recent study indicates the optimal asset allocation is probably a U-shape!
The Journal of Financial Planning research article finds that the optimal outcome is actually to increase equity exposure in retirement. Notably, though, this doesn't mean increasing the exposure up to 100% in equities. Instead, the point is that cutting equity exposure lower and then slowly gliding back to the original may be better.
For instance, a portfolio that starts at 30% in equities and is rebalanced for an additional 1% per year (such that it climbs to 60% in equities after 30 years) performs better than a 60/40 stock/bond portfolio that is just rebalanced to 60/40 every year, even though it has less in average equities throughout retirement and less in equities every year except the last (when it finally gets 'back' to 60%).
The authors test various stock/bond return assumptions, and the benefits for this "rising equity glide path" are modest but consistent, though the best glidepaths vary depending on return assumptions (not surprisingly, more conservative equity returns lead to lower overall equity exposures).
If returns are low enough and/or withdrawals are high enough, eventually the optimal portfolio is simply to own significant equity exposure and 'pray' for a good outcome, but for those consuming at reasonable 'modest' withdrawal rates relative to their wealth and returns, the rising glidepath effect holds.
The strategy is framed as a "heads you win, tails you don't lose" outcome, as in situations where equity returns are bad early on and better later the strategy wins (more conservative during the bad years, and dollar-cost-averaging into equities in the later years that are better), while if equity returns are good early on the retiree will be so far ahead that the retirement can't fail even if the bear market comes later with slightly higher equity exposure.
Overall, the research implies that the optimal lifetime asset allocation may look less like a flat line or a steadily declining one, and more like the letter U where equities are higher in the early years, glide down as retirement approaches, trough at the point of retirement, and then slowly start to slide up again in the later retirement years (albeit still not as high as they were in the early years).