If you connect an external PCIe expansion chassis to the Thunderbolt 3 port, you can install a multi-channel PCIe capture card in it, like the Decklink Duo, Magewell ProCapture Quad or Yuan quad cards, leaving your USB 3 ports for other uses. Some thunderbolt PCIe expansion units also give you additional USB3 ports, adding to your I/O options. Your laptop with 8th gen i7 and GTX 1060 looks like quite a capable unit which should be able to handle this.

I have owned an Intensity Shuttle for many years and have used it with vMix on occasions, either as an input device or an output device. It can be a bit fussy regarding USB chipsets and firmware revisions, but I use mine a lot with my current MSI laptop (with Intel HM170 chipset).

Recently I've been testing a Zotac AMP BOX mini external Thunderbolt 3 chassis, which can accept a PCIe capture card and has USB3 ports as well.

N7K_2213cs.jpg (206kb) downloaded 4 time(s).

N7K_2234cs.jpg (210kb) downloaded 3 time(s).

In a comparative test on a desktop PC, using both an internal PCIe card and a PCIe card in the Thunderbolt 3 box, plus a USB3 device connected to the motherboard USB3 ports (plus an NDI encoder), all devices exhibited similar latency into vMix at 1080p60. (i.e. They were all pretty much in sync with each other when fed from a common signal source)

QuadTest2-4Oct18.PNG (748kb) downloaded 31 time(s).

vMix Capture 04 October 2018 10-35-57.png (3,970kb) downloaded 9 time(s).