2. Writing IPS isn't currently the top priority, but I'll get to it.
3. Valid. There's nothing really new in ZP. I considered making a format with more power, with things like loops and multiple write types, but what would be gained from that? Simplicity is important. I see a format that takes half an hour and 75 sloc to fully implement applying and writing as a good format. That's what I tried to achieve with ZP. The good ideas were already there, so I adapted the ones that fit my goals.
But I made ZP for multips, not the other way around. It doesn't even require use of the ZP format at all; any comma-separated list of files on the command line is treated as a patch via diff. ZP is just a convenience around having to do that every time. multips is effectively a basic version control system. I don't know any other binary patch applier that is aware of conflicts, except perhaps Just F Patch in a sense. I've seen a lot of community projects flop, and I wanted to do something about it. multips is my attempt at that.