I like the self bailing floor idea, always made more sense to me in a raft like this than a spray skirt if it could be done for a reasonable weight. Also a seat with a back would be handy, often I just fold up a full length self inflating sleeping pad into a back rest/seat and that works ok in my current raft.
An inflation bag seems fairly simple once you figure out the boston valve portion? I use a garbage bag rubber banded to an adaptor currently (super light and replaceable) but I have a much different valve.
You can get multiple chambers via a zipper if you need to as well.