I don’t know your business model, but I imagine the more people use your card, the better. I don’t feel I would get enough out of a premium card to make it worth spending £ 5-10 a month. If on the other hand, all I had to do was pay a minimum of £5,000 per year through the card (or pay the £100 fee as a penalty) then that would tempt me more, plus I may change my habits to put more through the card.
But they already have this, flip it on its head:
Spend £120,000/year on your card in Europe or £12,000/year outside of Europe, or combination thereof, and we (Revolut) will waive the fee