British Airways had amazing business class fares that allowed use of stackable discounts this fall. Some people were booking business class tickets between the US and Europe for less than $500 in cash (plus points), for instance.
With British Airways devaluing its points back in April upgrades became more expensive from premium economy to business class for flights 2001 miles or or longer. But for upgrades from business class to first class you’re still paying what a coach award ticket would cost in miles for the flight with no cash co-pay. And even deep discount business class fares are upgradeable.