there have to be a huge software effort to port to a new boot sequence and work with a different (and completely incompatible) GPU.
Good point, as a hardware guy I keep forgetting the effort needed to do the software
Hardware engineers do tend to forget that...and that's behind a lot of issues with SBCs. Even the Pi had teething problems early on (remember the USB issues?), but other board makers, without the resources to throw at the software have struggled and generally not done as well.
So die shrink and maybe 1.5Ghz but still run cooler, overclock to 1.8GHz?
VC4 will run faster? USB change to USB-3.
I would think 1.2GHz with overclocks to--maybe--1.5GHz. At or above 1.5GHz you'd probably be in the mandatory heat sink region. VC4 faster...probably somewhat. The VC4 is heavily tuned to conserve power (and hence stay within TDP limits). I'm *hoping* for USB 3, as I think that is the current bottleneck on the Pi. Even Eben has indicated as much in at least one interview.
Maybe first pass just try current design on 28nm, no USB 3.
Well.... I am given to understand by people actually do chip design that a die shrink is *almost* as big a job as designing a whole new chip. That being the case, making changes to alleviate known bottlenecks would--at least--be very tempting and one would hope that swapping USB 3 in for USB 2 would be, not trivial, but close enough to a standard operation as not to affect the schedule very much.
Why do we need USB 3? Don't need it for mouse or keyboard.
Maybe USB 3 mem stick will make for faster USB boot?
USB 3 wouldn't be for speeding up boot (in the general case, speeding up the SD card interface would have more effect there), but for those who have network intensive tasks (and that would also cover...streaming H.265), it would make GbE possible, even if that isn't part of the design (so long as there is a USB 3 equivalent to the LAN9514 chip). For the subset of use cases that use SSDs, HDDs, or even USB sticks for mass storage, you could go (on an HDD) from 30MB/s transfer rates to 80MB/s rates (that's from tests I've run using a Pi3B and a Roseapple Pi, which has a USB 3 port). With SSDs, you can get up around 125MB/s transfers. On a Pi1, USB 3 isn't all that useful because there isn't enough compute capacity to *need* it. It's the faster CPUs in the Pi3 where the slow external I/O starts choking off the CPUs.
Not sure how hard it would be to go USB 3, but since the VC4 needs to be USB aware this could be the stumbling block.
Double the boot rom?
I'm not sure either. I don't know how different the VC4 would have to be as it would be looking at the internal bus.
2GB memory I think requires hardware change or cheaper chips?
Yes. There would have to be a change to the VC4, which can only address 1GB and--perhaps--cheaper RAM packages. There are SBCs with 2GB RAM for prices pretty close to the Pi, so the RAM can't be all that much more expensive, but the design of the Pi is extremely sensitive the price of its components. If it were up to me (which it isn't), I would try to design the memory interface to be able to handle at least 4GB, and--if I could get away with it--more, perhaps as much as 16GB. Note that is in no way a suggestion of a 4GB (or more) Pi, but a way not to have to redesign the memory bus circuits for a good ways into the future. For the initial builds, I would expect the RPT to stick with a 1GB board and increase the RAM as pricing and availability permitted, just as the Pi1 started with 256MB (and the Model A was originally slated to have 128MB!), and later got 512MB.
A die shrunk 3, that could actually be soon, it's been over a year since the 3.
Any other change will take longer, but they did say a year or two.
Split difference is 18months, mid year plus.
Any problems will add months.
Last year, when the Pi3B was launched, Eben said not to expect a new model for "2 to 3 years", so--yes--another 1 to 2 years. I would expect that the work on the "Pi4" SoC was probably at least in the planning stages at least 2 years ago. So figure 4 to 5 years from concept start to board. Note that it took about 7 years to go from the beginning of the Pi effort until boards went up for sale, and 4 years from launch until the Pi3B. So a 5 year development cycle starts to look what passes for normal.
Looking farther out, there is probably already ground work laid for whatever eventually becomes the Pi5.
Faster ARM cores = h.265 in software? Maybe 1080?
4K? not unless they have been working on it for a year already
Hmm, not much heard from the hardware guys in the news, have they been too busy?
I would guess that there are a lot of "irons in the fire". Don't forget that within the last year we've had the A+512MB, Pi2B2, CM3, CM3L, CMIO3, and the Pi0W, with the Pi3A still to come. So...yeah...I think the hardware guys have been pretty busy. And again, I think the next SoC has been in the works for at least 2 years. Whether or not it will have VC hardware blocks for H.265...dunno. I wouldn't rule it out. I also wouldn't rule out that it might be an individual license deal like unlocking existing hardware decoders.
Prediction Pi 4 Oct 2017 28nm, running cooler at 1.6GHz, VC4 bit faster too, no other changes.
I may be too conservative, but I would predict Pi4B in February 2018, 28nm, running cooler at 1.2GHz, permitted overclock to 1.4GHz within warranty, USB 3, 1GB RAM (but able to address more, without telling us), modestly improved VC4.