I believe the old ways, which agile destroyed, will come back because the implementation isn’t the hardest part now. Agile recognized correctly that implementation was the hard part to predict and that specification through requirements docs, UML, waterfall, etc. were out of date by the time the code was cooked.
I don’t think we’ll get those exact things back but we will see more specification and design than we do today.
Agile was a response to the coordination problems in certain types of firms. Waterfall persisted in organizations that have and require a more traditional bureaucratic structure. Waterfall makes sense if you are building a space probe or an unemployment insurance system, agile makes sense if you are trying to find product market fit for a smartphone app.