Financial modeling can take many different shapes -- personal budgets, investment tracking, BvAs, deal models, DCFs - the list goes on (and on). For many use cases, Coda will absolutely be a great tool with many advantages over spreadsheets. For example, you could keep track of a set of rental properties applying the same financial calculations to each one with column formulas for consistency, flexibility, and scalability.
However, for others (e.g. a Discounted Cash Flow model), Coda does not yet support common financial functions found in spreadsheets (e.g. NPV).