Personally, I would like to see more flexibility for pre-pay customers. I find that, over time, my requirements change as to what I need from my plan. Where as a few months ago I may have needed lots of texts, now I predominantly use whatsapp to message people, and therefore probably only use 50 or so per month, but my plan with o2 gives me 1000.
T-Mobile used to do something- which I believe was available on pre-pay and on contract- which gave you an amount of money for the credit you purchased, for example, £10 top up would give you £100, and everything you used your phone for came out of this.
So if your charges are predominantly for data, that's all you pay for.
It may not suit everyone as it is less black and white as to what you actually get for your money, but I like the idea of your plan adapting to your needs as and when they change.