I don't think it would be safe at all to try to resurrect the Nolan continuity -- and Bruce as Batman therein -- after it was brought to a rather decisive conclusion, let alone to suddenly transform Nolan's relatively naturalistic universe into the more fanciful one the Justice League would exist in. Let alone to try to continue it without Nolan directing, which he wouldn't. Any one of those could produce audience backlash. All of them together? I think that's a lot riskier than just starting over from scratch.