external sd - Use sd card as internal storage and stop writing to internal memory for good

Smartphones seem to die after two years of usage, as if they knew that you just have paid the last instalment.
The common reason seems to be the failure of internal memory.
I'm desperately trying to have my phone escaping from this cruel destiny.
The idea I initially had seemed simple, but the web didn't seem to share my optimism.
This is the idea:
- create ext4 partitions in sd card
- mount at boot sdcard partitions to /data and /cache (and maybe /preload and /efs if they ever get written)

I'd like to know what's wrong with this idea and why it cannot work, but the main question is:
Can I stop writing to internal memory for good?

I've seen all the apps out there (app2sd, link2sd, DirecoryBind, s2e , you name it) and all of them seem to relocate subdirectories, never the main /data .

Any help will be highly appreciated.
Thank you!