This is a fairly large project that is well under construction. It will completely reconstruct the interchange and replace the loop ramps with flyovers to create a directional Y interchange.
Website: https://www.rctc.org/projects/71-91-interchange-project/
Here's a video rendering of the project:
So this will be done before the southern part of 71 has been upped to six lanes. The crude 3D model video makes it look like the connectors between 71 and the eastern side of 91 will be one lane in each direction. I would think they'd be two lanes, but I can't find any maps on the CalTrans site that answer this.
Just as a reminder, this project is well underway and should finish later this year.
Again, here's the website link and they have construction updates with plenty of photos as well as a link to their Facebook page, which has a plethora of photos and videos. It's coming together very nicely: https://www.rctc.org/projects/71-91-interchange-project/
I'm wondering if someday the connection from 71 to WB 91 will be moved to the west of the new flyover, so that it has a more gradual curve, or if the AADT on that ramp is so low that it wouldn't be worth it.