Currently transactions received via a Stripe Account and can split, categorize, tag, etc…. but users cannot create a rule that applies to transactions in the Stripe Account because Stripe does not show in the list of Accounts that the rule could apply to.
In Simplifi, Stripe is a 'service that is activated'. For small business users, however, Stripe is an account like any other financial account. The business receives income there, pays financial institution (processing) fees there - all in the form of transactions, and also sets parameters around how often and where to sweep account balances into another financial institution account - daily / weekly / monthly and so on.
Speaking for msyelf, using Stripe as an account existed long before Simplifi. With Stripe being a primary account where both Income and Expense transactions are realized, it takes away the usefulness of Simplifi if rules cannot apply to it like any other account we use in our businesses. Please make Stripe appear in the list of accounts when creating rules.