Building off my previous suggestion, the achievement goal could stay relevant by resetting each year (or some other appropriate period). Because insurers can't practically let people run down their premiums forever (though 'running off your rate' is a catchy tag line), and the health benefits that justify the reductions require ongoing exercise, there needs to be a mechanism like a reset (or gradual rescaling) that encourages people to stick with the goal (or sign up for Everest #2) while still delivering value to all stakeholders- the employee, the company, and the insurer backing it.
Glad you liked them, it's an idea that could actually be applied to several of the concepts that won (Healthy Benefits and Health Leave could adopt some form of this model). Tying in the insurer not only provides clear rewards, but it also takes the administration and execution costs off of the company and puts them with the insurer (who at least theoretically is not in it to scalp people for a huge profit and should be on board with plans that reduce the likelihood of illness that will suck money out of the pot, allowing them to reduce premiums).
I think it is important to consider the administration costs of any wellness program because money spent by a company on employee is, at the end of the day, money the employees could be taking home in direct salary, returning to investors, or putting into development. Health care costs are a huge part of the stagnation of real wages so hopefully by bringing the insurer in everybody could win- the employee gets healthy and saves a little money, the insurers liability goes down, and the company gets more productive employees that it can both pay more and who, by being more productive, increase the value of the company.