I haven't seen any other examples yet of it being used on a lap steel. Jerry's new Lap King was likely the first, and it's possible it's the only lap steel with one so far. To make it work on a lap steel Lap King's Jason Dumont had to do a lot of customization to his Rodeo model, here is what he wrote about it on Facebook in June:
Here is a really interesting project made for Jerry Douglas. This lap steel features a transposing tailpiece made by Hipshot products that allows the player to switch tunings with the flip of a lever. Because of this it required the standard Rodeo model design to be tweaked a bit; the neck needed to be joined at the 14th fret marker rather than the 12th to give a bit more room.
The body was also stretched a bit at the bottom to give a nice platform for the tailpiece.
The pick ups are made by Lollar pick ups, in my mind the finest pick ups available. I really cant say enough about their pick ups. I have been using them exclusively for a decade now. Here I use their Supro reproduction "string through" design and pair it with their "Gold Foil" for the neck position. The guitar made it's debut with Jerry May 30th in Charleston S.C.
So Jason has the "template" now for use on one of his lap steel models, but any other builder is going to have to go through the process on their own to make it work with their lap steel designs as opposed to many of the large body modern resonator guitar designs where it it likely a pretty easy fit for most builders.
I have played the device a couple times on a friend's Beard E model and I think it's really slick, it operates very smoothly. But it strikes me as something you don't use all that often "on the fly." I think of it more like the original motivations for the pedal steel guitar as having the pedals for changing tunings as opposed to using the instrument for the string bending sounds we are all so familiar with.
As far as the position of the lever, I know I wouldn't want it on the bass side as opposed to the treble side, I think it would sort of be in the way. As for Jerry and the dobro, I estimate that he plays in G tuning at least 75% of the time, in D maybe 20% or more, and something else less than 5% of the time.
I was listening to his JD Band set at the Telluride, Colorado festival last summer on a streaming webcast and I recall him ending one song he plays in G and flipping up the lever on his Black Beard to D and immediately starting into the next piece. Historically he would have to unstrap and switch out guitars and tell a joke or comment on the crowd or the weather to make that move. Now it's like bam! - into D tuning - right now.
This is of course the main value of the thing, not to mention as a touring musician not having to haul around an additional guitar for a different tuning and pay more airline baggage fees.
You could certainly use it on the fly to change to the second tuning if for example you want to play the lead break on a song in the other tuning for variety, but I wouldn't think within that lead break you'd ever want to be flipping it back and forth no matter how adept you are at using the device. On a lap steel that's what some of the guitars equipped with palm pedals are for.
It hasn't been linked in this thread, here is a demo at Beard in Maryland which was shot shortly after the device hit the market a couple years ago. Paul had Gaven Largent come by and play a Beard JD signature guitar with the DoubleShot, I think this was the first time Gaven had ever tried the thing himself. He's not doing this in the video, but if one is going to change the tuning in the middle of the song you are going to want to mute the strings with the palm of your bar hand so that you don't hear the change in tuning.
Gaven is the young man who replaced Rob Ickes in Blue Highway going on a year ago with Rob leaving the band after about 21 years to concentrate on his duo with Trey Hensley.
https://www.youtube.com/watch?v=3FP_Zw30ZpY
