This was always possible, I own multiple books for kids which have obviously been made with random clip art and illustrations which are badly paired.
But proper illustration is so much better, I doubt it will go away.
Perhaps a better simile is hand made clothing: you can get mass produced stuff, or you can get small batch, or you can get handmade. There is a market for all of those.
Proper illustration is so expensive that in most cases people are tolerating it because the alternatives are either very horrible (random clip art) or to make do without illustrations.
If digital tools enable decent clipart that can be at least somewhat paired to the content, that will take over most of the market, because then it'll be just somewhat worse than proper illustration while being dirt cheap in comparison.
The market for all of those is ridiculously lopsided, though. That doesn't bode well for illustrators, especially the ones that pour love into crafting every drawing and sketch to make it as good as it could be.
But proper illustration is so much better, I doubt it will go away.
Perhaps a better simile is hand made clothing: you can get mass produced stuff, or you can get small batch, or you can get handmade. There is a market for all of those.