Feature Request: track post-acquisition revenue per acquired-user cohort over time

Feature request

Is your feature request related to a problem?

When using marketing analytics, I would like to answer questions over time, e.g:

• "Of the users I acquired through Google Ads in April, how much have they spent by July?"
• "Are users from campaign A still purchasing months later, while users from campaign B churn after the first order?"
• "Is my CAC justified once I look beyond the first purchase?"

A customer has framed this request as "Would it be possible in the future to have an LTV dashboard where we can track how new users perform over time and whether they continue making purchases?"

Marketing analytics today is built around period rollups: cost in a period, conversions in a period, ROAS in a period. There's no concept of an acquired-user cohort that you can follow forward in time. ROAS, as currently computed (conversion value in period / cost in period), only ever reflects revenue that occurred in the same period as the spend, which materially undersells channels that take longer to pay back.

This is a gap for any customer with a multi-purchase business model: e-commerce with repeat purchases, subscriptions, marketplaces, B2B with expansion revenue.

Additional context

Ticket: https://posthoghelp.zendesk.com/agent/tickets/54247 (moved to PostHog: https://us.posthog.com/project/2/support/tickets/61097)

Debug info

No implementation files, tests, or entry points are named. Start by reviewing the existing marketing analytics period rollups and the linked support context to define cohort acquisition, attribution, and revenue requirements. Done means a dashboard can follow acquired-user cohorts over time and show their later purchase revenue and retention.