You've correctly said that the best thing is proposing better example questions that wouldn't be a good fit on either site. As a regular EE.SE user there are probably a few things I agree with on your list, but some that I don't. Running through them and using the newest questions at the moment under each tag so I'm not being biased:
assembly - Doesn't really have to be related to hardware, Stack Overflow has plenty related to user-mode programming for a PC and Could an ARM (ARM7TDMI) Branch instruction take 6 cycles? seems to have fared pretty well on EE.SE.
bootloaders - I've answered a few myself, never seen a close vote on one (apart from generally poor questions) and the latest one How to update MCU bootloader? is answered and has no close / down votes despite being a little vague.
kernel drivers - Agree while not specifically off-topic on EE.SE for hardware drivers it's probably not the best place to get an answer, and harder to search because the tag related to voltage / current drivers. Having said that not all kernel drivers are hardware related (file systems for example) so there might still be a lot of expertise on Stack Overflow that's relevant, but otherwise probably a good one for Embedded.SE when it relates to hardware drivers.
embedded C that uses pointers - Embedded C questions are on-topic at EE.SE as long as they relate either to hardware or a resource limited processor, otherwise Stack Overflow is better. The very last C tagged question was closed because it was a poorly defined request for a UI library that said the hardware hadn't been picked yet, but the next one What happens when you fall off the end of main() in a PIC? is answered / upvoted even though it turned out to be a duplicate. But regarding pointers in particular as long as they have an embedded aspect because of architecture / FLASH etc they normally go well on EE.SE.
USB/similar implementation specifics - The last question What exactly does OTG_FS_SOF do? Is it vital or imperative to USB host mode? doesn't have an answer yet, but nobody is rushing to close it. Some fairly high-level questions like What is a product ID in USB and do I need to buy it for my project? have proved popular.
FPGA Programming!! - Looking for the last one related to programming and ignoring one that was part of a long string of horribly formatted gimme-the-codez questions from the same user the next one is Using Digital Clock Manager with Verilog to generate 25Mhz clock from 32Mhz internal clock. Once again I've never seen a close vote on one apart from the questions that would be unwelcome on any SE site.
OS Porting - Agree this might be a good area as long as you avoid anything too broad. Specific hardware / programming questions though would be OK on EE.SE / SO though. But questions about builroot for an ARM and cross-compiling and such things would be good topics.
Exposing Processor specific features to a kernel - I'm not 100% sure what this means because the kernel will normally have access to specific processor features, but assuming you mean using those features to enhance / change operation of the kernel that's probably another good one that doesn't fit existing sites.
I'm not being negative on the proposal just highlighting you will have a lot of overlap problems to overcome initially. I agree with Gilles that the best questions may be ones that involve integration between platforms and higher-level design questions that wouldn't really sit well on either SO or EE.SE.
For things like Linux hardware device driver programming while there may not be a lot of expertise in the area on EE.SE at the moment it's incorrect to think that experts will magically appear for a new site and I don't think good questions in that area would be closed EE.SE, even if they went unanswered. I think most mature SE sites have on-topic and heavily upvoted questions without answers just because nobody happens to know the answer.