Yeah I agree with most of the stuff on your list. I doubt the iPad Mini would be updated in the spring. I think they will keep it around as the cheaper option every year, with a slower chip. Not sure why they did that last year, but the iPad definitely won't go back to a spring upgrade cycle. They were missing too many sales during the holidays because of this before.
That's a good point. I wasn't around here during that time (I was taking a break from Apple rumors) so I didn't know the reason why they switched from spring to fall. In that case the iPad mini would be avoiding an update for 2 years, which seems a bit too long. Maybe it'll get a very small update next week with Touch ID (like what Ming Chi Kuo predicted) and/or a price drop to replace the A5 iPad.
Unlike with the 5.5" iPhone, rumors seem relatively silent on an iPad mini update so in any case I don't expect an update as large as for the iPad Air.
I have a theory that Apple might use the spring to launch new iPad Pros so that they can test out chip technologies in advance for the autumn iOS device lineup. Not necessarily always something like an A9 chip (year ahead), but stuff like new WiFi chips, advanced Touch ID scanners, new RAM configurations, more of the mundane stuff that they can try out ahead of time. Maybe even advanced GPU options. I think a Pro would definitely have something like an A_X chip. I think that's why Apple stopped marketing iPads as having A_X chips. First of all the device are similar in power now, but second of all they want to differentiate the high-performance iPad Pro from the rest of the devices.
I generally expect (after the first update or so) the iPad "Pro" to have the same update cycle as the rest of the iPads, but if the Pro is considerably different from the other iPads and/or is targeted differently then I can definitely see them on a consistent spring update cycle (after all, the MacBook Air and MacBook Pro usually aren't updated at the same time).
I have also been thinking about possibilities in A
nX chips, especially regarding the GPU. Since an iPad "Pro" would likely be, by default, the "top dog" in the iPad lineup, I would expect it to have the overall most powerful hardware. An A
nX chip in an off-cycle (compared to the A
n update cycle) has the unique challenge of facing A(
n+1) chips while still using the same CPU core family and possibly GPU core family of the A
n chips. For example, if an A8X uses the GX6650 and an A9 uses some graphics that are 50% more powerful than the GX6450 in the A8, then the A8X may only end up tying the A9 in graphics performance. I wouldn't be surprised if future X series chips have more on-chip custom hardware (which can be doable because the X chips presumably have larger die budgets) that add more features. Also they could be an opportunity to try out new process nodes on established CPU and GPU cores (although I'm not sure how custom hardware factors in).
As for Intel chips, I was referring to Broadwell in spring 2015 and Skylake in autumn 2015. Broadwell is the tick (new process, 14nm) and Skylake is the tock (new architecture on 14nm process). The way I understand it, Intel had problems getting the new 14nm process up and running, and so the Broadwell chips were delayed until spring 2015, and that pushes them up against the Skylake release in autumn 2015, which Intel has said they are still planning on for a release date for Skylake even with the delay of Broadwell. So I'm planning on a Skylake Mac upgrade late next year.
I would think that Apple would update the Mac Pro with Haswell first, then Broadwell, but with the update cycle of previous Mac Pros I'm not too sure about that. Maybe we'll see a surprise Haswell update next week then a skip straight to Skylake if the Skylake-EP processors are coming soon enough.