Uses for SPI Flash
yes, it would be possible. it's possible technically - booting from SD works - the things left are 1) ensuring SPI flashed firmware isn't prone to bricking the board, and 2) making it understand PCIe/NVMHCI, of course. 
as an example, for the illustration, you download the image of your choice and it is provided not as a plain image, but as a live image, that being first run out of an SD card, gives you opportunity to either run as a live session (for familiarizing) or start installation. if the installation has been chosen, the installer then lets you choose the OS installation target device (eMMC, NVMe SSD, or even USB storage - because why not for SBCs, the latter is not kewl for a laptop though). then it asks you of whether you want to install/update firmware and if you do, again, it will give you choice (theoretically, apart from SPI, it could be eMMC, with the boot areas includingly! however this is too optimistic - not all ROM codes understand reading eMMC boot areas, anyway, general purpose area is always ready, and even an SD card - but one probably won't want this scenario for the laptop). and finally installing/updating all these things where needed. this is a whole installation procedure, not that easy (and dumb) as dd-ing, it's harder to accomplish, but it has advantages, for example, it would take care of proper initializing GUIDs inside a GPT partitioned drive - they, GUIDs, need to be unique for every disk and partition in the whole Universe, rockchip already uses the GPT scheme, but of course dd-ing violates GPT badly. and many other benefits. but it's only an example intended to clarify the answer to your question. also, when things get even more developed, it will be possible to update firmware through the fancy firmware user interface. ^_^ in short, it's possible. as I understood, the main obstacle is lack of NVMHCI support in uboot. using eMMC as an OS installation target is a good solution. you of course still can use NVMe SSD for your data.
as an example, for the illustration, you download the image of your choice and it is provided not as a plain image, but as a live image, that being first run out of an SD card, gives you opportunity to either run as a live session (for familiarizing) or start installation. if the installation has been chosen, the installer then lets you choose the OS installation target device (eMMC, NVMe SSD, or even USB storage - because why not for SBCs, the latter is not kewl for a laptop though). then it asks you of whether you want to install/update firmware and if you do, again, it will give you choice (theoretically, apart from SPI, it could be eMMC, with the boot areas includingly! however this is too optimistic - not all ROM codes understand reading eMMC boot areas, anyway, general purpose area is always ready, and even an SD card - but one probably won't want this scenario for the laptop). and finally installing/updating all these things where needed. this is a whole installation procedure, not that easy (and dumb) as dd-ing, it's harder to accomplish, but it has advantages, for example, it would take care of proper initializing GUIDs inside a GPT partitioned drive - they, GUIDs, need to be unique for every disk and partition in the whole Universe, rockchip already uses the GPT scheme, but of course dd-ing violates GPT badly. and many other benefits. but it's only an example intended to clarify the answer to your question. also, when things get even more developed, it will be possible to update firmware through the fancy firmware user interface. ^_^ in short, it's possible. as I understood, the main obstacle is lack of NVMHCI support in uboot. using eMMC as an OS installation target is a good solution. you of course still can use NVMe SSD for your data.
ANT - my hobby OS for x86 and ARM.
