I wonder if GM is still concerned that 6.6kw charing will degrade the battery unacceptably faster than 3.3kw. Tesla and Nissan don't seem concerned. For those who change cars every 3 to 4 years it's no issue. However, GM has to be thinking about possible warranty issues at the 6 or 7 year mark. I don't know if the evidence is clear yet.
6.6kW/17.1kWh ~= 0.386C. Flat, highway speed driving is something like 12-15kW so close to 1C, and hills mean even higher C rates.
So, the answer is no, it won't be a problem. They went for 3.3kW charging because 3.3kW is all that's necessary for overnight charging and 3.3kW saves money, space and weight. Similarly, the current Spark EV only has 3.3kW charging because they re-used what they had.
If they are serious about PEV, and at all serious about releasing a BEV in the future, they'll understand that they need 6.6kW+ charging systems anyway. Also, since the Volt 1 was released, power electronics have already become cheaper, smaller and lighter, which means 6.6kW should be easier.
Also, if they take a look at the market I hope they will understand that people like the EV experience and they don't burn gasoline for fun.
Putting that together, I'm hoping that Volt 2 will at the very least have an "Extreme EV" option package available, including 6.6kW charging, heated rear seats and a lower ERDTT setting, that will really make the Volt an EREV.