Part of the reason why I'm vegan is because I'm lactose intolerant, a(n at the time) distressing genetic quirk I picked up from my Chinese mother. Asian people have an increased propensity towards lactose intolerance! Chinese culinary tradition is well known for its soymilkyness! I can buy warm soy milk on my way to work for breakfast on cold winter mornings from little street stores! So you would think, given this, that finding a soy coffee in Beijing would not be that difficult.
Sadly you would be wrong.
It is, however, the only place in Beijing that you can buy a soy flat white (not even the New Zealand inspired Flat White Cafe does a soy flat), and I'm willing to put up with a lot for such a delight.
And you can bring your keep cup! However alas Serk is not open Mondays, and not open before 11am, so it is useless for an on my way to work coffee purchase.
Other than Serk, it's sadly lattes all the way. I go quite frequently to the Vegie Table on Wudaoying Hutong, where I can get the world's largest soy latte (or a latte with coconut milk, which is fun). They don't do takeaway but if you bring your own cup they'll whip something up for you. This coffee is nice enough but it always leaves me with a funny after taste.
Starbucks is funny here, it's mostly considered a bit of a dessert place, the most popular drinks seem to be the ones with lashings of cream on the top, and I know of business people who take their clients to Starbucks for a bit of after business lunch dessert.
Don't go to Costa Coffee for a soy coffee. They use Asian soymilk, which is definitely not the right thing to use in a coffee.