Hi,
In HikaMarket, you can configure "extra categories" (in the HikaMarket configuration and per vendor).
We got a feature request ticket in our HikaMarket TODO list in order to add the support of Groups for the "extra categories".
So, in the function "getExtraCategories" in the HikaMarket vendor class, the extra categories could be read from the accesses settings depending the current groups of the vendor.
A subscribed vendor would be in a specific category ; which give them an access to the "featured" category.
And becayse your "featured product" will pick up products in that category, you will have a big part of the feature.
The missing point is that when a vendor subscription end ; a plugin should be triggered in order to remove the products from that "featured" category.
One other kind of solution is to use a custom plugin which will add a new "task" and a new button in the product edition toolbar.
That plugin can propose to add (or remove) a product from the featured category if the vendor is a subscribe vendor.
And like for the other solution, the plugin should remove the vendor products from the category when the subscription ends.
The first solution is nearly available but it will allow vendor to put all of their products in that featured category, without any limitation.
Having a custom plugin to add/remove products is interesting in the way that you can have a better control ; I know that website makes the vendor pay to place their product are featured (by making a special purchase or using credit points).
So it's hard to give you advice like that...
Regards,