It is remarkably premature for even the most long-term planning in Loudoun to be dependent on Metro going to places like Moorefield Station. The saga of "Rail To Dulles" is a story politics, machinations and greed, and Loudoun County has only been the most marginal party considered in the negotiations.
Fundamentally, there is a conflict between proponents of the above-ground "aerial" option and the below-ground "tunnel" option through Tysons Corner. The aerial option has three main advantages. First, it is already approved and on the books. Building an above-ground track through Tysons Corner would mean simply continuing the process already started. Second, the aerial option has the support of major players in the decision making process. And finally, the aerial option means Federal Funding. The Tunnel option puts FTA money, already at some risk due to benefit/return calculations, potentially off the table.
However, there are significant problems with the aerial option. First, many of the people who would actually take the metro strongly prefer a tunnel. Second, tunnel proponents are going to court to prevent construction of the aerial option. And finally, the contracts and money behind the aerial option are cozy to the point of being fishy. The aerial option was issued as a no-bid contract to Bechtel. Bechtel is the same company whose contracts in Iraq were deemed so corrupt the government cancelled one - for a desparately needed hospital.
And this is all before official construction plans are even in the approval stages.
It is for this reason that we should not expect to be taking the train from Loudoun to Washington anytime before our first graders have graduated college. (And this at a time when the average American will move over 11 times in their life.) But many development plans for Loudoun County, such as Moorefield Station and Loudoun Station, are predicated on the Metro.
Any and all development in Loudoun, for at least the next four years, must stand on its own, independent of any plans for the Metro. Furthermore, if and when the Metro does come, Loudoun's taxpayers must reap the benefits as much as landowners will. That will possibly mean revisions to tax policies to address the gains on real estate values, or much more aggressive proffers. In either case, it will be the Board of Supervisors in ten or fifteen years who needs to deal with these issues, development today must be considered for the value, and costs, it will yield today.
[update]Loudoun County Traffic has a post on the Speaker of the Virginia House of Delegates' opinion on rail in northern Virginia: "an incredible waste of money."