I'm familiar with one of the products that offers that (a mortgage coupled with a HELOC, and a sophisticated program that advises owners when to transfer funds from the HELOC to the mortgage). It actually looks like it works.
I say that because some people worry about scams. Some people worry, understandably, that "If it sounds too good to be true, then it isn't." Still, the program I'm familiar with (and I think there are a few others out there) are getting business.
On the other hand, yes, that pitch does have a certain appeal. Some people just like to have their mortgage paid off. Or they like to track how much their mortgage has declined every month. And even though, in some cases, financially it might be better for someone to have a mortgage (for a tax shelter), some people just don't want a mortgage hanging over their heads.
As you know, those plans require the owner to have some discretionary income. Problem is, in today's market, that pool of owners is smaller; you'll get a lot of calls from people who not only are upside down mortgage-wise, but don't have the discretionary income necessary.
A word of caution: Some real estate firms discourage their agents from promoting those plans. I don't know how they'd feel about agents allowing others to pitch those plans. I'm with a major real estate firm in the Eastern U.S., and we received a memo a few months ago cautioning agents about involvement in such programs.
The program I'm aware of encourages its people to "buy" the program for themselves. If you've got the money and are considering it, I'd suggest trying it out yourself. See how it works. If you're comfortable with it--if it seems to work the way it's promoted--then give it a shot by promoting it to others.
Hope that helps.