What the what
I have not read the light novels, or the manga (is there a manga?). I came across this article while searching for news of season 4. Does this sound legit, or is this some fanfic? I would really like a season 4.
Unless they are going with completely original content no. The light novels are barely a year after S1 as far as DxD timeline goes.
DxD EX is definitely something that exists. It's a six part mini novel that was released with each vol of Born in Japan and is about Issei's kids. If a 4th season does happen, I'm very certain it will adapt the next two LN volumes, and not some 20 year time skip
20 year time skip
It would be a greater time skip or Issei got a girl pregnant pretty quickly more than once in a short span of time, lore says it takes like 10 years of trying. Given how the hero faction is organized they wouldn't dare ally themselves with Loki, its against their ideology. Heck they wanted Loki out of the way!
Then again the LNs are not in the same timeline as the anime is. So whatever.