There have been rumors swirling for a while that Google is planning on adding support for Windows 10 on Chrome OS devices. The inclusion of Intel silicon inside the new Pixel Slate instead of ARM hints that Google still has plans to support Windows dual-booting on Chrome OS.
https://www.notebookcheck.net/Intel-inside-the-new-Pixel-Slate-hints-at-future-Windows-10-support.337812.0.html
So it lacks mobile LTE connection because Intel solution requires additional chip to achieve that unlike ARM that have built-in support.
Clever move :-)