I'm sure they will improve, however I think they should have fixed more bugs in 8.1 then they did. In the last week, my phone has resprung four times running Safari. Now wether or not Safari has a memory leak is completely unknown. It could also be due to the lack of RAM in the iPhone 6. Before everyone jumps on my back here, yes iOS is very memory efficient and to me, spec sheets are nothing. However, 1GB seems to barely be enough to support these phone since it at least half (most of the time 2/3rds) is being used when the OS is idle with no apps open.
I'm also not saying that Apple forces obsolesces on iDevices, however the engineering team should have added the extra RAM for the reason where if the user has multiple apps open the phone may not have time to write the app out of memory and the phone or app crashes. Would 2GB have completely solved this issue? Maybe not, but it sure as well wouldn't be as big of a problem. The extra RAM would also allow iOS to have more background processes running for system services. Think of how many more background services iOS could offer with a full 1GB RAM for itself and 1GB left for apps?
I have to disagree with you on the A5 devices getting iOS 9, however I don't work for Apple so I cannot say for certain.

Apple could always do a mid-year refresh of the iPad line, see the 4th Gen iPad. 3rd Gen was introduced in March/April 2012, 4th Gen came out in October/November 2012.
If the A5 lives to see another year, I will be genuinely surprised because then they would also have to support the iPad 2 since the iPad mini 1st Gen is really just a scaled down version of the iPad 2 (even the same resolution, but higher pixel density due to smaller screen). iPad 2 will be the first, and probably only iDevice to ever see five iOS updates (5, 6, 7, 8, and 9). Worth mentioning that the iPad 2 was the first iOS device that got four updates as well.
I can agree with you that the iPad mini 3 might end up being another iPod touch 4th Gen, but as of right now its more like the 5th Gen iPod touch or 1st Gen iPad mini in the fact that its a new device with last years chip. Its also comparable to the iPhone 5c; the fact that it has the same internals as an older model with an extra feature or two and a revised casing.
I still personally believe Apple should have at least thrown an A8 into the iPad mini 3. Not even an A8X, just the A8 found in the new iPhones. At least it would have
some sort of speed increase over last years model and people would have a greater incentive to get the new iPad mini. The best deal in the iPad line is really the iPad mini 2. Its $50 more then the iPad mini 1 with much improved performance, and $100 cheaper then the mini 3 which has the same internal specs.