My take is that wet shaving (or if you like, the return to traditional shaving) will continue to be on the rise. I also believe that there will soon come a moment in which the whole thing will explode and will become a fashion. That of course cannot obviously last very long, if and when it happens.
When some of us started full time shaving something short of a decade ago, the vendors out there were few, and the whole thing was starting to grow. Of course every market is different - for example in North America orders of magnitude are absolutely different when compared to anything else in the world. In the last 10 years we went from traditional tallow-based soaps to veggie products, we are now full of artisan soap makers, and we have also seen a rapid rise in small manufacturers who make stainless steel razors.
But that's for the purists, up until now. The average consumer out there is not like us here. Volumes and numbers may not change much for the purists. However if we start to talk about the market in general, I feel that the current trend with beards and absence from shaving (that's been going on for some years, especially in Europe) will stop at some stage. That will be the moment when the average consumer, the bulk of the market, will discover and turn into wet shaving. I believe that when this moment comes, sales of DE razors and wet shaving/grooming specialized products in general will more than quadruple.
I'm sure that giants like P&G or others have done research on these things and do have market data, as well market forecasts of course. Here in Greece for example we are currently experiencing an intense growth of 'barber shops' that offer grooming/shaving experiences. Obviously it is a matter of debate how many of these 'shops' know their craft as should, and at the end of the day the subject market is so tiny with respect to the rest of Europe that it is insignificant even to talk about it. Already in the local flea markets you can't find vintage Gillettes on the cheap, as you could three years ago. Anything that surfaces is immediately swept by antique shop dealers.
The big break will come when one of these disposable celebrities or a few pro athletes start to wet shave. These are the factors which can drastically turn the general public into such a hobby. For long or short-term, we'll have to see, though...