The plastic gets brittle and more and more parts will start to break.Are you responsible for replacing it, legally?

The linoleum was so old the top skin was brittle and breaks off leaving about an eighth of an inch of hardened something? 

Neil,If not maintained (and maintenance is quite low) linoleum can crack when it is old - as does vinyl when it becomes brittle.  

Which get brittle and need replacing.  

That looks like PVC pipe , it will work , but its UV sensitive it will get brittle over time.

I am starting to regret this decision as this engineered hardwood flooring is so cheap and brittle it was clearly not worth it. 

The existing plumbing are the old polybutylene pipes that become brittle over time (30ish years) and are prone to developing leaks.  

Zinnser bin says on the can not to use on large areas as it becomes brittle in that case.  

New electrical is better than real-old electrical with cloth insulation but not as good as 30-40 year old wiring with thicker copper wire and thicker plastic sheathing, so long as the sheathing isn't brittle. 

You find it in 1950s era flooring tile (usually the 9x9 ones), concrete/asbestos siding (durable but brittle), piping insulation, sometimes that 1920s insulbrick siding, as an additive to some old plasters, and probably half a dozen other places I have forgotten.