Apple has been burnt by its reliance on other companies for modems, so to avoid issues with dual sourcing and even sale bans Cupertino wants to design in-house modems. This has already started under the leadership of Johny Srouji, the SVP of hardware technologies.
Srouji has been at Apple since 2008 when he was a lead chip designer, working on the excellent A-series chipsets and later on the proprietary chip used in the AirPods. The company has posted job listings in San Diego, which just happens to be the home of Qualcomm.
Dont expect to see an Apple modem in the 2019 iPhones or even the 2020 ones, development will take years (and hundreds of millions of dollars). Especially since the modem will have to support not only the well understood 4G, but the emerging 5G tech as well.
In the end, all of this could end up saving Apple money Qualcomm charged $30 for a modem and wanted $7.50 in royalties on top of that (these royalties are part of what triggered the legal war). Also, integrating the modem into the chipset is more power efficient (thats the case for Snapdragon, Exynos and Kirin chips chips).