I have the solid Double Cut 594 and a Hollowbody ii with the 58/15 LT's too. If the HBii had the options of coil splitting, I wouldn't be gassing so hard for the Hollowbody 594. I personally believe that the Hollowbody is more of a difference than just taking more wood out than the Semi-Hollow. To me, the Semi-Hollow doesn't really make too much of a difference and the biggest factor is more the weight. It does feel more resonant but it didn't change the tone that much - at least I didn't feel it made a significant difference.
A lot of that has to do with only using the Mahogany for the sides - a Slab of Mahogany that has the 'middle' cut out to create the sides rather than using thin mahogany strips that, using steam, are shaped as Acoustics and a lot (if not all) Hollowbody guitars are made. Instead of using a laminated sheet that is steam pressed to create the 'carve' body, PRS use a slab of Maple and carve it - also for the back too. The Maple top and back is why I think it makes more of a difference than just removing more mahogany to turn the 'semi-hollow' into a hollowbody.
A marriage between my 594 and my HBii seems like the perfect combination. If I had the opportunity to spec my own, I would seriously consider swapping the tune-o-matic type bridge for an adjustable Piezo bridge (like the HBii has) but keep the 24.594 scale and Pattern Vintage neck - as well as the 594 individual tone/volume pots with coil splitting and of course the 3-way on the upper horn. It would add a mini toggle (to go from Magnetics, to blend then Piezo only) as well as the Piezo volume/blend. It would mean having the the two output jacks and Battery compartment but would be more versatile. I guess I don't need that as I do have my HBii for the Piezo and if I bought a HB 594 with Piezo, that could make my HBii redundant.
As it stands right now, with my very limited space and really pushing my limits on the Guitars I can actually fit in my tiny apartment, I would actually squeeze a HB 594 in because I love the look, especially the look of the carved and stained maple back with no plastic back plates - as well as the sound of the 58/15 LT's in a Hollowbody, the feel of the Vintage neck carve, the scale length etc and buying one would be more of an indulgence than a 'need' as I don't know that I will get much use out of the Split options and therefore I already have the main sounds with my HBii. I can justify owning all my guitars to me, someone who isn't gigging, because of the 'unique' tones I can get, the expansion of my tonal palette which is why my collection is small but also each guitar is significantly different.
A HB 594 though really does excite me and whether I can get the opportunity to buy a Piezo loaded HB 594 or not doesn't change the fact that I still want one regardless of what it adds to my collection, regardless of whether the reason is as basic as just wanting one rather than justifying it because I don't have 'something' that I may want/need. I blame PRS for making such desirable guitars that I want just because they exist rather than what they may add to my tonal Palette.