This has come up from time to time. Just using a <picture> tag, without any other changes, wouldn't make any difference, of course. It's not magic. What might make a difference is actually using it to serve up different image sizes, based on the dimensions of the visitor's device, using the srcset attribute.
There's nothing stopping a skin developer from doing that. The jAlbum core produces only thumbs and slides - it doesn't automatically crank out multiple slide sizes, for example. But a skin could easily do this on its own.
But at least some of us think that this is a solution to a problem that is about to be OBE - overtaken by events.
If you're using a phone on WiFi, you're probably already getting all the speed you need. My Android phone, connected to my home WiFi, loads my image-heavy pages almost as quickly as my big, hard-wired desktop.
On a cell network, more and more providers are offering unlimited data (remember when your talk minutes were limited?), and on a 4G network, download speeds are hovering between 5 and 12mbps. That's already fast enough to handle typical jAlbum slide images without much strain. And early indications are that 5G networks will be topping 150mbps. At that point, concerns about image file sizes will start to fade away. Your web host probably can't cough up content that fast, anyway.
I had a revealing experience a few months ago. In a rented beach house I was visited by an old friend, a working architect. He fired up his laptop and was toiling away on it when it occurred to me that I hadn't given him the WiFi password. He said he rarely bothers with WiFi any longer. He has a dongle for the laptop that is, in effect, a little cell receiver in a box. For him, that's easier than messing around with WiFi in places like airports. Mind you, this is a user who isn't just checking his email. He's connecting to his home PC to retrieve things, and he's jerking around large architectural renderings and CAD files. On a 4G network, he gets all the speed he needs. It was an eye-opener.