It’s now commonplace for Silicon Valley entrepreneurs to turn their domiciles into startup incubators. Three years after Kenna started 20Mission, its 41 rooms are booked solid. A small room with a shared bathroom now runs $1,800 a month. Stays can last years but are typically a few months. Today every room has a door, and the front door unlocks with the tap of a smartphone. Rent is paid in cash, check, or Bitcoin. The Internet router takes up an entire closet. In the basement there’s a television studio, where residents produce a weekly Web program called Money & Tech.