I'm surprised by people's votes for not at all - surely Sony is interested in making money cheaply. These are the same people who released 4 PSP revisions and 3 PS3 ones. Not to mention that the Vita got a revision despite not being very successful in the first place.
Although I agree that they might choose to revise the base PS3 one more time over revising the Pro. If they revise both they will have 3 SKUs at the time of the PS5 release which can be confusing for consumers. In terms of costs and late-gen milking, though, I do not see how a PS4 Pro slim is not a move they would consider.
Well, the thing is, a Pro slim doesn't make much sense if there's a superslim and a PS5, as the Pro would be squashed between the two and sales would thus be too low to make it worthwhile for Sony.
However, if Sony would make a slim Pro and discontinue the base model, removing it's competition at the bottom, then it would make a whole lot more sense. Even then, the slim Pro would still need to be below $300 to be worthwhile, otherwise, the price difference between itself and the PS5 would be too... slim.