Very few current papers (I don't know of any) are developer incorporated, Ilford stopped producing the developer incorporated versions of Ilfospeed/Multigrade quite a few years ago, and we all know Kodak stopped theirs too

It was an hidden fact that the early Ilfospeed papers could be processed using the Ilfoprint Activator/Stabiliser machines and I used one for a few years, I mixed up an Activator from scratch NaOH, some sulphite and KBr, and used Hypam instead of stabiliser. The sulphite & KBr were needed to prevent base foggingg in the activator.

The reasons for Developer incorporation were to improve speed of processing and allow very short development times, but with almost no large scale B&W print processing left there's no need.

There were disadvantages because you couldn't use processing techniques like soft working or contrast developers to to vary print contrast on the fixed grade papers.