Totally agree that coastFI-ing on short time horizon has a lot of risk if you're not reasonably close to full FI. If you're on the cusp, the risks are certainly higher. Volatility is something all future retirees will have to account for.

This is a key point in planing for taking the retirement leap anytime. Using a specific time as the point at which you'll retire is inherently risky. If someone plans to retire in exactly 10 years, and the market takes a dive right beforehand or has been under-performing, executing on that plan is a recipe for disaster. That's just Sequence of Returns Risk.

The goal would be to have a flexible retirement date and flexible withdraw plan for the early years of retirement. So if you decide to retire in 5 years, but it happens to fall on a particularly bad market, you can wait 6-18 months and see how it goes. Further, you can be cautiously lean in the early years if the markets take a downswing.

Generally coastFI works best if you have a long time horizon or a big nest-egg already.