Obviously, phone owners should be able to set these limits and not have them dictated by a corporation.

But I still want to hope that this could be a first step to remind developers to build efficient and optimised apps.

Giving users a way to limit memory consumption per app won't solve this, it can only be solved by limiting it on the grand scale and that will never happen, if you give people only the means but no defsults. I think, the most sensible way would be to set default limits but ultimately the phone owner decide which limits to set.