I don't remember when the last time I carried "cash" in my wallet or shirts pocket.

So true man I rarely carry cash and the only time I realise that I am short on cash is when a vendor says he doesn't have UPI which happens like once every couple months.

As for scams happening via UPI there is a new system coming out where you can reverse a UPI transaction if you have either being scammed or have sent money by mistake. So yeah that issue could be solved later down the road.