If I were assisting somebody make the jump from extract to all-grain, I would first ask how much they want to make. Less than 3 gallons, I would show brew in a bag, ~5 gallons + I 'd show them Denny's batch sparge techniques. I like BIAB for small stove top batches, and it is a razor thin margin.
I would do the same thing except that I would recommend continuous sparging instead of batch sparging for larger batches. Becoming a proficient continuous sparger ensures that a brewer will most likely never have to learn a new sparging technique if he/she decides to become a professional brewer.
With that said, what we are doing when we promote our favorite technique is acting as evangelists. There will come a time when someone in the U.S. steps up to the plate and evangelizes BIAB like Denny did with batch sparging. It is just a matter of time. I do not want swell Denny's head, but without his evangelism, batch sparging would be just another way to sparge. I remember when batch sparging was not part of the home brewing lexicon.
There are product manufacturers who are already jumping on the BIAB bandwagon by making products that are designed to brew larger batches using the technique. UTAH Biodiesel is offering large stainless steel mesh baskets for BIAB brewers.http://utahbiodieselsupply.com/brewingfilters.php#biab
With that said, I see a day when five gallons will no longer be the standard batch size. The batch size was chosen mainly due to the availability of 5-gallon fermentation vessels. What we will see is a migration to larger and sub-5 gallon batches. The ratio of 10+ gallon brewers to five gallon brewers is much higher today than it was when I started brewing. I remember when Jim Busch (BURP and Victory Brewing) was the talk of the town because he had a one barrel brewery. Today, a barrel-size system is nothing special.
The thing that has taken me completely by surprise is the rise of the 1-gallon all-grain brewer. On the other hand, it is amazing that it took this long for the concept of brewing 1-gallon of all-grain beer at time to take hold. It seems so logical considering that it can be accomplished with normal kitchenware.