(Fritz von Titz approves this post)
SHIV is based on the same graphics engine as SHIII. They just upped the pretty so to speak because cpu's can handle it better than in 1995. With that thought in mind why not combine the two? They (Ubi) could easily and cheaply update SHIII to SHIV standards of graphics quality (I think somebody here has already modded SHIV special effects and eye candy to SHIII) So its do able. Just add one more thing (Japanese career?) throw it all together in one executable and walla SHV!