Lots of business plans are quite vague about what is to be done in future, and but I'm pretty sure, YC will ask questions on customer acquisition routes and cos

Lots of business plans are quite vague about what is to be done in future, and but I'm pretty sure, YC will ask questions on customer acquisition routes and costs, [planned] revenue model, development priorities, long term growth aspirations, when the product will come out of beta and what they'd spend the cash on. They might not require a bullshitty chart of next year's P&L, but if you already have a clear idea what the metrics that are supposed to lead to it are (growth rate, CAC vs CLV, untapped market size) you'll be at an advantage and if you can't tell a plausible growth story about your most likely route to growth you won't (not even if your deck has the chart!)