Just buffer the power and be done with it
Grid WILL have problem one way or another. They have the only means to regulate it - offer reduced price off peak - like at night. And that is going to be a problem once all the guys start charging at night.
So what is solution? Simply put additional battery packs at home (and at work, and definitely - in "gas" station) and charge them when you will and at whatever pace you choose. And while you are at that - put that silly diary tablet computer away from silly humans and closer to smart batteries. This way it can "negotiate" the best deals on electricity with electric company or take advantage of silly wind mils when the wind actually blows...
Sort of electricity stock market.
In the end if YOU need to be prepared for urgent trips then you say to your system "charge ASAP" - it will draw power in peak time and it will be expensive, BUT this would not upset the grid balance as this very act would (generally) cause peak rates to increase and off-peak to decrease for other customers so they may shift off-peak and restore the "perfect" load balance.
How would you manage this "electricity stock market" and enforce dynamic price for electricity to the customers is entirely another matter, but it definitely much more worth investing research dollar than silly idea of everybody syncing their bathroom time with world plus dog...
Of course it would still work as it is with just two electricity tariffs. Dynamic prices are just a further convenience. You (power company) can (and probably would be forced) to calculate them yearly, but making it every month, day or minute would lead to power company dream - ideal load 24x7 and best price for electric company and each and every customer.