I actually think this 'delay' happen early to mid 2017, after Kodera took over. This is just my theory but I think Kodera looked at the then current design of the PS5 and ordered some design changes and/or additions to the design. I think Sony saw where the industry is going (more service oriented) and decided to promote Kodera (precious Network and Services boss) to be President, and in turn PS5 design philosophy changed around that time as well.
I think one of the big changes was PS3 emulation (native PS4 BC was in the PS5 plans from the get go imo). Idk if you guys remember this:
https://www.theregister.co.uk/2011/02/28/sony_toshiba_ps3_chip_plant_sale/
Sony had to buy an entire factory just to continue making Cell and rsx chips. This was for the PS3 and the chips continued to be made for PS Now servers. They even had to redesign the Cell for PS Now server racks:
https://www.eurogamer.net/articles/digitalfoundry-2014-sony-creates-custom-ps3-for-playstation-now
Cell continues to be a (costly) thorn in Sony's side. The chips make it difficult for PS Now to easily and quickly expand. If Sony is able to design PS5 hardware to properly run all PS3 games, they will finally be able to relieve themselves of the Cell. Right now, PS Now needs separate server hardware to run PS1-PS4 games, adding costs and possibly halving capacity and hardware bandwidth for PS3/PS4 games. Imagine if they are able to design a PS5 hardware that can emulate PS1-PS3 games and natively play PS4 (+PS5 obviously) games. Hugely reducing costs, and the ability to quickly expand PS Now service as long as TSMC is able to pump out the hardware needed.
Going into the FGPA talk, I think the positives of including it in the hardware heavily outweighs the negatives for Sony in this case. This is basically what MS is doing with their hardware design for the nextbox, but instead of adding specific hardware just for games like Sony is, they're thinking about interprise apps.
Ps. If you look back I'm at my comments way earlier in this thread, I've been suggesting that Sony might be doing this way before the MS 'leaks' came out.