A couple years back I donated a 2GB SD card made by SanDisk to science.  I setup a simple loop which continually wrote to the card with pseudo random sequences until it filled the card.  It would then read it back, verify it was correct, erase the card, and start over.  I got 11TB worth of writes before the card started showing failures.  I have no idea if this is typical but lets assume it is.  A 64GB SD card would be more like 700 TB of writes, which should be sufficient for a decade of blockchain usage even if the tx volume increases by a factor of ten or more.  

Of course one advantage of a dedicated device is you can strike a compromise between storage writes and memory usage.  One example would be to only write confirmed tx to the memory "disk", the memory pool would remain in memory.  Blocks are occasionally orphaned so with enough memory you could delay writing the block to storage until it is x blocks deep in the blockchain (each block deeper becomes exponentially less likely to be orphaned).  Other temporary less critical data like information on current peers, can be batch updated to storage.  If the node goes offline between updates it isn't a critical that the stored information about peers is slightly stale.  The fact that Bitcoin is a decentralized network makes it easier to implement delayed writing.  You can always request recent information from peers again.

The main scenario to avoid with flash is using it as a high throughput "RAM", but even a memory constrained device, will have some memory so there is no need to write everything to flash.