If the whole rumor of Sony wanting to use Vega but changing it Navi is true , 2 things should be considered:
1. Navi was not developed for Sony or 70% of AMD engineers were not working with Sony R&D for Navi.
2. Sony wants a more powerful console .otherwise Vega would have been cheaper and the could have launched in 2019 and getting a 10 million lead on x2.
I don't think that rumour rules out the WCCFTech roadmap/reporting (1. above), in fact I think it can dovetail neatly with it.
Here's one timeline that makes sense of both. Speculation in italics:
Fall 2015 - work begins on PS5
2016 - AMD reveals roadmap with Navi on it, slated for 2018.
Between 2015 and 2017 - Sony works on a target of a Fall 2019 launch based on Vega (on the supposition that Navi would not be 'console ready' until a year after its first products, and perhaps too risky to pick at this point)
Late 2017 - Sony decides to move the release of PS5 to Fall 2020
(I don't believe they could have put the brakes on that target any later than that. They'd need at least 18 months of dev kits etc. to be out there. If Sony had waited longer than this, we'd have heard about this 'first version' of PS5)
In moving to 2020, Sony wanted something more than Vega, and more than the original Navi planned for 2018. AMD says OK - and decides, rather than releasing two new chips within a year, to delay Navi and make bigger changes than originally planned, to meet Sony's needs, while stretching Vega longer than initially planned.
Jun 2018 - WCCFTech reports Navi as a new microarchitecture, has been delayed a year (now due in H2 2019), that Su put 2/3 of their engineering talent behind it, and is being driven by Sony's timing and needs for PS5
In other words - I think that rumour can fit neatly with the WCCFTech reporting on the Navi roadmap and Sony's involvement, and might actually explain - at least partially - why Navi was delayed, the conflicting rumours about what it actually was etc.
I think the idea that Sony made a last minute switcharoo that's forcing them to use a 'Navi/Vega hybrid' does not make sense of anything of what we've heard to date. If Sony changed their plans from 2019 to 2020, it happened years ago.
