Parliament is dominated by Islamists, not nationalists as they've all been labeled ba'athists. I've been called ba'athist several times, let alone senior people who lived through Saddam's time.
I don't think any merging is possible, the merging that took place under Abadi's leadership was nothing but putting PMU heads into positions of political power that's why it went so flawless. In the end these are two conflicting political blocs. However obviously most PMU members aren't going to fight their own state, army. But they surely wouldn't mind orders to overrun, attack the US embassy for example.
With or without America, it's important the army grows and gains further control of the PMU. We can't have the state within a state for the long-term, it's a joke. A very rich country has been reduced to a playground for militia's led by some turban wearing uneducated monkeys. On top of that we have ISIS terrorizing the entire area and Kurdish thieves going wild.
Saddam, as much of an animal he was and how much misery he created for all of us. Today's rulers have drawn an image of themselves even worse than Saddam's.