Did you find any solutions for this? Looking for something similar. This is the closest method I can find from my research but not sure it’s good enough.
Create a product ‘Free anytime shipping’ for 1 year which customer pay for.
When purchase is complete, add a tag to their customer profile.
Use a third party app to display different shipping rates to these customers such as Bespoke Shipping ($15 per month).
This third party app is necessary as if you simply create and hand out annual shipping codes to customers who buy the product, then they will not be able to benefit from other promos as discount codes can’t be stacked.
Little late to the party, but since I’ve seen that people are still looking for a solution..
One of my clients was also looking for a solution, and we didn’t find any good native solution. So we created our own app and also made it public for others to use. The name is CustomerCards. The cheapest plan is 7.99 and has a free trial.
You can just create a simple “Amazon Prime”-style product, and tell the app that every customer that buys it should get a membership awarded for a certain period. During this membership, they get shipping discounts automatically applied. There is even a small UI you can show on the customer profile page, that shows the current membership status and validity.