@casaschi and @Kunga both make valid suggestions, either would potentially be better for your average user without exposing Revolut to excessive ATM costs and, not as restrictive as 200£ (which is even worse given the loss in relative value over the last year)
I think the limiting number of transactions may work out better for all concerned, whilst also making the user think whether their withdrawal is strictly necessary.
Also, where possible, Revolut should charge flat fees for withdrawals outside of the limits, I’ve seen mentioned elsewhere, that one of the problems behind a flat fee approach is with the ATM itself but, perhaps if Revolut passed on where ATMs charge flat fees, that would inspire confidence in Revolut’s actions.
Furthermore, why not help the users to help you? By now, with the historic transactions you have to hand, it must be possible to compile a list of the ATMs that are most/least friendly towards Revolut (plus whether they charge % or a flat fee) and, this is something that will improve over time, with that detail users could try and direct their business through specific ATM groups over others and, as a result, reduce the costs to Revolut and make it possible to have higher limits - everyone wins.