Has there been any update on this gratuity feature? My business needs this too as a party and entertainment facility. We tried just adding a new product each time we had to add a grat on to an order, but soon stopped because our inventory was getting flooded with miscellaneous "Gratuity" products, so we wiped them all out and have just added the amount on to the card through an external credit card processor. This however, is now proving to be troublesome as we've had some party parents refute the card charges on their accounts since they don't match their receipt (which due to lack of gratuity ability, is missing on their charge receipt).
After several years of online existence on Shopify, we just began a brick and mortar only to realize this huge hole in the system. Also more suprised that Shopify has remained unresponsive for so long over the numerous demands by various sellers for this basic feature. We might have to switch to Square for our offline sale after all.