This is a well-framed question, and I think the answer hinges on a distinction that OFAC's Cuba regulations make—or rather, fail to make—between the underlying transaction and the payment rail.

1. The import authorization is broad but conditional. § 515.582 authorizes "all transactions, including payments, necessary to import" goods and services from independent private sector entrepreneurs (IPSEs). The operative word is necessary. If a U.S. partner is importing software development services from a Cuban IPSE, paying that entrepreneur is clearly "necessary" to the authorized import. The regulations do not specify the form the payment must take. OFAC's general position is that sanctions compliance obligations "apply equally to transactions involving virtual currencies and those involving traditional fiat currencies." That cuts both ways: it means you cannot escape sanctions by using BTC, but it also means a BTC payment can be a valid payment method if the underlying transaction is authorized.
2. The problem is the definitional gap. § 515.340 defines an IPSE as a Cuban national who is not a prohibited official or Communist Party member, and who owns or works for a small private business, is a self-employed individual (cuentapropista), a private consultant, a small farmer, or a private cooperative of up to 100 employees. The definition is broad. But the regulations do not address how a U.S. person is supposed to verify that a specific counterparty meets this definition when the payment is made in BTC. There is no KYC equivalent for a peer-to-peer Bitcoin transaction. This is where the "no guidance" problem you identified becomes operationally significant.
3. The September 30, 2026 amendment makes this harder, not easier. OFAC amended § 515.584(h) to remove the authorization for U.S. banking institutions to maintain accounts solely in the name of Cuban IPSEs. As of that date, banks must block those accounts and require a specific license to unblock them. This signals a tightening posture. If OFAC is restricting the most transparent payment channel (bank accounts), it is unlikely to look favorably on a less transparent one (BTC) as a substitute, even if the underlying import is authorized.
4. My read: The transaction you describe is not categorically prohibited if the import itself falls within § 515.582 and the counterparty genuinely qualifies under § 515.340. But the burden of demonstrating that both conditions are met falls on the U.S. person. A BTC payment does not eliminate that burden; it arguably increases it, because OFAC's strict liability standard means you can be penalized even for an inadvertent violation. The ShapeShift settlement ($750,000 for 17,183 transactions with Cuban users) shows that OFAC enforces this aggressively, even against non-U.S. exchanges.
5. The libertarian framing you set aside is actually the crux. You said you are not thinking of BTC as an evasion tool. But from OFAC's perspective, a payment method that bypasses the banking system is definitionally harder to monitor, regardless of intent. The regulations do not prohibit BTC payments to Cuban IPSEs explicitly. They also do not authorize them explicitly. That silence is not permission—it is ambiguity, and ambiguity in sanctions law is resolved against the person subject to U.S. jurisdiction.