PSM got nuked because of the Rejuvenate hack (Allowing for native Vita usermode homebrew), and Nintendo would just be creating a whole lot more trouble for themselves, which will only add a lot more to what has already been achieved in the 3DS hacking scene...
The closure of PSM hit Sony and existing PSM users quite hard if I'm honest, with users now not being able to redownload their paid PSM apps due to non-existant PSM servers now.
And if Nintendo create something similar to PSM, and new security holes get found in the software which lead to new exploits, just like PSM, practically the same thing will happen. ¯\_(ツ)_/¯