Well, I beg to differ, and I'll tell you why: I started using Photoshop and then Lr as you and others recommend years ago, but I always found that because the output spaces that the photos are destined to are almost invariably narrower than "the widest gamut working space you can", I always found myself re-editing when it came to purposing the photos.
You beg to differ with who about what?
All editing in LR and ACR take place in a variant of ProPhoto RGB and thus it's color gamut, there's no way around that. Now if you've got rendered images in a fixed RGB working space that isn't ProPhoto RGB gamut, despite this fact, you may wish to consider if:
1. You want to edit them in the ACR engine and....
2. If you should have kept them in ProPhoto RGB from whatever source (usually raw) they came from. Hence my recommendation: Edit in the widest gamut working space you can.
That aside, you want to make a print (from any RGB working space of any sized gamut). Now you soft proof with the paper profile and select a RI you desire and based on that preview, you decide
if you wish output specific edits and move forward; either as a Proof Copy (keeping the original without those output specific edits) or in Photoshop with a layer set with the output specific edits for that one output. You might have half a dozen layer sets for a dozen paper/printer combo's. And you keep all off until you need to use them. As you can see, this is far easier and more effective in LR using Proof Copies.
So no, I don't nor believe I've EVER recommend soft proofing from the get go. The opposite: make the image appear as you desire, as best you can, ideally with raw and metadata edits in the widest color space you can. Then when you're ready to make a print, soft proof and based on that, create output specific edits. All described in the video(s) I've produced on the subject.
Gamut size or otherwise, the output color space differs from the working space just based on RI among other factors. So you have to soft proof just to pick the RI for printing,
then, IF necessary, you can edit that soft proofed '
copy' (VC or otherwise). That means, at the step in the workflow when you're ready to make that print, never before.
And no, the output space can be larger and narrower in some areas of color space than the working space. No printer can produce
all of sRGB color gamut. The sizes and shapes of the two greatly differ.