The issue really isn't the phone itself for Sony (at least how I see it). Personally, I believe Sony's issue has been a lack of identity among its consumers regarding its mobile devices. Apple has an iOS and the whole ecosystem going for it, Samsung is the current champion of Android. All Sony needs to do is utilize their PlayStation OS on their own mobile devices and that should be the tipping point for Sony to be viable in the smartphone market.
Since the PlayStation brand is already a proven commodity among the mass populous and phones like the Z5 premium are stellar technological marvels that already have PS4 Remote Play capability, the move should not be that difficult for Kaz-Sensei, Shu-Sensei, Totoki-Sensei and the other sensei's to discuss upon. Sony will most likely be getting more profit than what it is now.
Just my opinion though, and I am sure I could be wrong, but Sony already has experimented with a singular ecosystem with the PlayStation brand in some capacity. I am sure expansion would not hurt; attempting to do so anyway.
This is exactly what Sony needs to do. PlayStation OS should be running on every TV, Smartphone, Tablet, Blu-ray Player, Camera, and gaming device that Sony sells. They should have a feeling of connectivity and similarity across the brand. This way a consumer knows what they are getting when they buy a Sony product, and they know that all of their purchases, and all of their devices work in harmony.
Like you said, Sony has to get off of the me too OS, because S*****g already owns that market. They have to set themselves apart from the competition, and give people a reason to switch from S-Phones or A-Phones. PlayStation already has a strong ecosystem behind it, an devs already have experience with cross platform development, and cross buy. All Sony has to do is open up PlayStation Development, and allow more proffessional non gaming companies to release their apps/software on the PlayStation Store. They won't compete with the market leaders from day one, but with a little investment, and good marketing, PlayStation OS and PlayStation Hardware could be close to leading the market in the next 5 years.
Stop hate, let others live the life they were given. Everyone has their problems, and no one should have to feel ashamed for the way they were born. Be proud of who you are, encourage others to be proud of themselves. Learn, research, absorb everything around you. Nothing is meaningless, a purpose is placed on everything no matter how you perceive it. Discover how to love, and share that love with everything that you encounter. Help make existence a beautiful thing.
Kevyn B Grams
KBG29 on PSN&XBL