They talked about it in a interview:
Overwatch PvE Modes
turikk: Every year, we get questions about a PvE mode from a bunch of people. Do you guys have any updates on a permanent PvE mode outside of events?
Jeff: It’s something we’re super interested in. If you look at our team makeup; Scott Mercer, Geoff Goodman, they were two leading designers on WoW who did loads of awesome boss fights. Then we’ve got Mike Heiberg who did loads of StarCraft campaign missions. There’s a huge PvE pedigree on the team and we’re super interested in it, but the thing people sometimes overlook is that our engine is built from the ground up - and it’s brand new. There are a lot of different ‘moving parts’. Even getting the smallest AI to path and move across the map is a big deal for us. We know people want a PvE mode, but when people ask us to make our current modes permanent, we don’t feel they’d be replayable enough. To get to the point where PvE is its own thing, in that regard, is almost like talking about a new game. We’re going to continue doing cool stuff like Junkenstein; but at its core, Overwatch, the game everyone’s playing, is a 6 player action shooter.
Source:
https://www.reddit.com/r/Overwatch/comments/7bdyby/blizzcon_2017_interview_jeff_kaplan_bill_warnecke/
I hope the developers will eventually add a permanent PVE mode in the game.
They were talking about how difficult it is to program it, but maybe did they had a breakthrough with the upcoming PVE mode from the event.
