I don't care about an ultra thin phone. Manufacturers make them crazy thin, then a lot of people put them in a bulky case to protect them.
Make a thicker, plastic backed, non water resistant, non dust resistant phone with a swappable battery and I'll be happy. Heck, I'll buy one for each member of my family.
Other than being gimmicks, I don't see the actual value of being dust/water resistant or being thin.
You ruin your phone because you dropped it in water. Your fault. Be more careful.
You ruin your phone because you got it too dirty. Your fault. Be more careful.
These things aren't needed, just used as excuses to make a $800 phone a disposal device because they sealed the battery inside.
Even though I hate my LG G4 with a passion. And have had three catch fire out of nowhere. At least I can swap the battery when needed. For the same reason is why my old Note 2 is still in service today.