School capacity is not an issue, according the county's own calculations:
SY2017-18 Enrollment thru 2026-27.pdf
...this shows that 3 of the 4 schools in the area will decline in enrollment in the next decade, and the one that will grow, Ritchie, will be at 88%
The issue is 300 more homes on the edge of Brookside vs keeping the land, which sits on Brookside's doorstep, industrial. It won't stay undeveloped.
The county says in its own planning documents that growth should be focused in service districts, and Vint Hill is the best property in the largest district for this. The US census says Fauquier's population will be 28% more in 2030 than it was in 2010--people want to live here, and while you can control how much sprawl there is, you can't just shut them out at the Prince William line. Putting homes here, vs out in a field outside a service district, seems to make sense. Plus they have their own water and sewer at Vint Hill.
With the care center and OVH coming, there will be demand for housing--for employees--besides single-family homes. Why not put some of it right in the community, and eliminate an industrial lot at the same time?
This seems like a solid plan to focus a bit of development in an area ripe for it, and have it concentrated with other development (Brookside).