The Theme Review Team is taking action to curb obtrusive notices that fall within its purview – those generated by themes hosted in the official directory.
During this week’s the meeting, cited Storefront, WooCommerce’s flagship theme, as one example of a theme-generated notice that does not follow the core design pattern and is shown on every page.
Another example is this style of activation notice on the Noto theme from Pixelgrade (header image).
In the past these notices have not been expressly forbidden, although they are generally frowned upon by those who want to keep the WordPress admin from being overtaken by large, branded notices and calls to action.
There don’t seem to be any specific requirements that would restrict the use of branding within the admin notices as long as they follow the core design pattern.
This new requirement will affect many popular themes on WordPress.org and will likely be applied the next time existing themes go through the update review process.
Themes already known to be in violation of this guideline will be prompted by the TRT to change their notices as soon as possible or risk suspension.