Personally I think Apple would be wise to make 32GB the base model. Flash memmory has been dropping is cost, and I doubt it would harm the margins all that much. Being able to get a 128GB iPad for $700 would be a big seller IMHO.
It would cut into their profits tho... They make an extra $100 while costing them only about $8?. I believe they will be the very last to make 32gb standard if they ever do it. There are a lot of driod tabs/phones that come standard and even some windows but Apple will be the very last.
Keep in mind they also make money off their cloud storage for people who buy the 16gb and then figure out they dont have enough room.