Apologies if it’s already been raised but how about flexible benefits for Metal and Black subscribers? For example Metal has 100 points to spend, Black has 50 points:
Travel/gadget insurance is 20 pts
LoungeKey is 20 pts
Each cash back retailer is 10 pts
So Metal could have 10 cash back retailers or insurance + 8 retailers.
That way subscribers can really get the benefits they value from their fee.