There are high chances for the Inquisitor to not be brought back
1)The Inquisitor like the warden is a non clearly defined character and is also highly customizable unlike Hawke.
The warden was not reused for the same reason and not because it could have been dead,this was actually mentioned in several interviews,BioWare was unable to replicate their personality.
Care to share those interviews? Because I remember clearly reading interviews where it was specifically mentioned (like one for PC Gamer) that one of the biggest hurdles to bring a character back (any character, not just PC) is the number of variable endings or states (which they internally call "quantum states") a character can have. And there's no character who has more quantum states in the history of the franchise than the Warden. Way more than Inquisitor or Hawke at any rate.
Gaider in interview with VGS also mentions that at the time they released DAO they didn't know if they'd be able to continue with the franchise - hence the variety of variable states AND epilogues that later turned out to be a huge problem for them to write around for DAI.
The fact that the character is harder to bring back if they die, even if optionally, was also mentioned in Biofan interview with Patrick Weekes. Weekes also mentioned in one of the panels that the reason they don't bring the Hof is because their story and usefulness for future narrative is DONE.
Which, judging from Trespasser, is entirely not what happens to Inquisitor.
2) The Inquisitor is a relatively unpopular character and BioWare proved time and time again that they cut unpopular characters.
Why i said it is unpopular?
For the simple reason that i read every source from fans(not just Bsn or the Blanketfort) and the vibe is quite similar many players don't like this protagonist which would most likely make DA4 unappealing for them.
You base your entire argument on the premise that people who claim they enjoy Inquisitor "don't read any other sources than BSN and Blanktfort" - which is simply not true. Even in internal or fan pools that were about bringing back Inquisitor to DA (in any role) around 75% is for 'yes', while the game popularity indicates that they either like the character or story well enough to enjoy it.
And I mentioned already the popularity of Trespasser DLC - it wouldn't be selling as well if people didn't care about character almost a year after base game's release, or would have a different reaction to the clear implication that BW is not yet done with Inky.
3)New players don't care about an old protagonist which does not have a clear personality,why BioWare should forced on them their "canon" Inquisitor?
You only make a "clear personality" distinction, because you *know* that new players can care or can start to care about recurring characters. The success of franchises like ME clearly proves that.
Plus - if newcomers don't care about character "with clear personality", why should they care about anything about any character or the story? Which they'd be playing a 4th installment of. Dragon Age isn't "The Elder Scrolls" franchise - at this point recurring themes, plot points or faces should be expected even by newcomers. Plus the requirement to make them interested with it doesn't lie with re-playing the previous games, but strength of he story or game. I was personally hooked in by DAI. I "didn't care" about past titles or any characters, "clear personality" or no, only for DAI to change it
Also - what makes you think that they'd bring a "canon" Inquisitor? There were already many ways that were mentioned here that could allow us to control and define the character, especially on dual-protag route.