What with the concern over the younger generations seeming lack of interest in gardening this prediction would seem out of the blue, but I think vegetable and fruit gardening is going to become quite fashionable over the upcoming years. Vegetable gardening would seem the obvious area of interest in gardening for most people, including the younger generations. It's will just take the right series of circumstances for it to go viral. The interest in organic food would seem to indicate that organic is likely to go mainstream, if it hasn't already. The next step from buying organic would be growing organic. In the not so distant future it will be a source of pride to have a dinner party with organically grown food from the garden. What with the interest in eating local food, you can't get any more local than that. "Those delicious squash we're organically grown, BY ME!"
So you have two big trends that will work toward the resurgence of vegetable gardening, the organic movement and the "buy and eat local" movement. There is another movement, the "slow food movement", which advocates eating our meals slower and savoring the flavors of the food and enjoying the company of friends. Its more about the process than the end result, food in our stomachs. In addition to the slow food movement there is the whole eating healthier movement which means eating more fruit and vegetables. As people realize that home grown tastes better they will have more reason to grow their own since you can extract he greatest flavor from home grown.
There is also the self-sufficiency idea of vegetable gardening which is quite empowering once experienced. "I can grow my own food" is a big draw for many people who feel they have lost the ability to fend for themselves. It empowers. I am not talking survivalist thinking but more like someone that installs solar panels so they don't feel be-holden to the utilities. Its liberating.
From the interest in growing vegetables will flow an interest in gardening in general. Once people realize that they can change the world by growing their own food they will gain an interest in landscaping the yard. They will find that by planting this or growing that they can impact peoples emotions. It will become fashionable to have areas in the garden that are designed to affect how we feel and react. Meditation areas, inspiration areas, energy areas, calming areas, play areas, romantic areas, etc.
I feel we are on the verge of a whole new renaissance in growing our own food. Not just for survival, but for the aesthetic, social and physiological benefits that growing our own food organically brings. When it's all said and done, it will be the outstanding flavor and pride that comes with growing your own that will really get people on the bandwagon. Until you have tasted the difference between a home grown tomato and store bought one you wont understand.