While I would have to hunt down the sources, as far as that recent Resetera leak goes, everything falls perfectly in line with conversations with Itsuno over the past couple of years. Shortly after DMC4SE dropped, Itsuno said in an interview that if it does well, then he will be approved for DMC5, also implying pre-production had begun. That quarter, DMC4SE was the best selling game for Capcom, so that in particular lines up perfectly with the leak when it comes to timeline. In supporting evidence, Itsuno only works on two series right now, Dragon's Dogma and Devil May Cry. While there is a want for Dragon's Dogma 2, Dragon's Dogma 2 already exists in Japan via Dragon's Dogma Online, which still has a lot of demand over here to be ported, though Capcom has expressed no interest in doing so anytime son, but maybe one day. That MMO continues the plot and digs deeper into the lore while maintaining, and enhancing, core mechanics introduced in the original game. We know Itsuno is working on a new game though, so when it comes to what he could be working on, it is very very unlikely that it is DD2, so this leaves either a new IP, or DMC5 to be the front running option. All signs point to DMC5, so as of current, I will be taking these rumors as true.
There is also some more potentially supporting evidence. The idea that the game will not be revealed at PSX due to Sony wanting to release a massive amount of content at E3 2018 seems very viable. Sony has confirmed that PSX won't be as big because of this concept. Just as well, youtuber EpicNameBro recognized that the Demon's Souls servers, which are run by different companies in each country that supports them, are all shutting down February 28th, 2018, which is a month before the end of the fiscal year for most companies. Hidetaka Miyazaki in the past has said that a Demon's Souls remake is not out of the question, just very difficult. With E3 peering right around the corner of the end of the fiscal year, and with Demon's Souls servers dying, it seems likely that we may see a remake at E3. This alongside Death Stranding and DMC5 would easily be the eggs Sony needs to "win" E3 next year.
Overall, E3 2018 will be a helluva time