On the ultimate question, I think whether the IVSB makes a good travel camera depends on whether you can accept the idiosyncracies of Barnack-type bottom loaders (including finicky loading and squinty viewfinders). I can and happily use Barnack-type cameras for travel when I want something sturdy that's also compact and can take different lenses. I almost always use an accessory viewfinder with the IVSB2 (or IIIc), so in the end the squinty vf isn't much of an issue for me, and I appreciate the compact size of the IVSB2.
IMO, the Canon P is a fine camera if you shoot mainly 50 or 90/100 focal length lenses. But if you're primarily a 35 user, and you wear glasses, you will find the framelines on the P hard to see: they're pushed out to the very edge of the viewfinder. In that regard, the Canon 7 viewfinder is a better bet; it's got a lower magnification than the P so the 35mm framelines are easier to see and frame with. The Canon P is noticeably larger than the IVSB (the Canon 7 is bigger still). However, the P is currently very affordable on the used market, so if cost is a concern it may be a very attractive option for you as a travel camera and to get back into rf shooting.
I sold my P after I acquired a Leica M2 and found the latter much easier to shoot a 35 lens with. But I missed the sleek design of the P, so last year on a whim I picked up a Canon L1 from a member here, and have been happily shooting it since. Unlike the P, the L1 uses variable vf magnification for 35, 50 and 135 focal lengths, so no framelines. The L1 also has a cloth shutter, compared to the steel foil shutter used on the P. The shutter is as quiet as that on my M2 (which is to say very quiet). Otherwise, the two cameras share the same sleek design, easy loading, and rugged build quality. I think the L1 represents a better alternative to the P if you're primarily a 35 user; if you primarily use 50, then it's a wash between the two Canon rf bodies, IMO.