Several modular retail kiosks are coming to the Bay Area's 44 BART stations. This should add extra convenience to BART's 400,000 daily users. There will even be a companion app to the retail pods that would allow passengers to run errands such as dropping off and picking up laundry as part of their trip. These types of services could go a long way in helping people get out of their cars and utilize public transit more.
Perhaps instead of using kiosks, retail can be fully baked into the design for the upcoming BART Silicon Valley Phase 2 extension--especially since the bulk of those stations will be located in the Downtown San Jose area.
The retail kiosks are already operating in Downtown San Francisco and will reach five more stations by the end of the year. Square footage is going to vary from 600 SQFT at Union City to 2,172 SQFT at Castro Valley. I imagine that San Jose's Berryessa station will likely be towards the larger end of the retail spectrum given the station's size and location.