I was tired all day, so, planning rather than wild prototyping. With the Mythic stuff, I have four systems. I'm leaning toward giving each of them their own package, but I don't know if that'll lead to problems.
Putting that aside, covering the question of Rank. Rank is used in various parts of Mythic, and my inclination is to turn it into a union of three types. "Raw Rank" ranges from Minuscule to Superhuman. There is also Superhuman Plus, and Minuscule Plus. Characters can have Ranks that are Raw, or Superhuman Plus. Rank shifts can adjust the ranks to anywhere in the full range. The Plus ranks have an associated number, which, to be consistent with the Fate Chart, has a minimum value of 2. The Plus ranks calculate an adjustment factor from their number; for the Raw ranks, this number is just 0. The overall adjustment is the acting rank adjustment minus the difficulty adjustment. Odds and Chaos Factor map to a Raw Rank, and those are then used as input to the fate function.
Back to the character sheet, there are seven default attributes, as well as allowances for customization. There are also abilities, which are more freeform. Attributes and abilities are given a rank of at least minuscule. Strengths and weaknesses consist of a name, rank shift (number from -3 to 3) and description (when it applies, and what it applies to). Rank shifts must be applied at user discretion, from the point of view of the code. There are also notes (this should be a module provided by the base package), and favor points (this should be a distinct module). There's also "summary", which I'll stick on the main Mythic module for now, but it might move to its own thing.
Besides that, I don't need much I haven't already implemented in some form. I need to be able to track the chaos factor, and I think for that, I'll implement an idea of "party" that the player sheets can point to, and that'll hold the chaos factor.
I've worked out a bunch of stuff to sink my teeth into. I should get on this tomorrow afternoon. For now, sleep.