I've got to echo the sentiment of Joost de Valk. The theme directory — and the plugin directory — should recognize the reality that developing quality themes and plugins takes financial investment, that there are upsells, and thus provide a mechanism for upsells to standardize the process.

Standardizing would allow classifying and quantify the types of things being sold (3 theme templates, 7 blocks, etc.) and it would allow the directories to provide searches that could limit themes to only those that are "fully free", only those that "cost < $xxx" and so on.

Allowing users to filter for "fully free" themes encourage more people to publish fully free themes because they would be more discoverable.

It would also give Automattic a revenue stream because they could offer the payment mechanism and take 10% or less of the cost of the theme or plugin.

It would create a much better user-experience for those users who do choose to upgrade.

It would make it easier for vendors to monetize, and it could also allow WordPress.org to limit ratings of paid products with paid support to those who have actually paid for support.

It would solve a myriad of problems that the strict "only free" mentality has created.

#jmtcw

BTW, I don't sell themes or plugins so I have no dog in this hunt other than as a user.