One can actually make a small mini-ITX based system
This case Thermaltake Core V1 goes a long way
It can take a full length GPU like 1080/1070/1060 and still be small. Well, it will not be mac mini small but very much manageable.
Since Nvidia has released Pascal drivers for mac, I have got everything working in the above case just that I prefer the black version of it.
1. CPU: Intel i5 6500
2. Motherboard: MSI Z170 Pro Gaming ac Mini-ITX
3. Case: Thermaltake Core V1 (Black)
4. PSU: Thermaltake 650W
5. RAM: 2 x 8GB DDR 4 3000 Mhz RAM
6. BCM94352Z NGFF M.2 WiFi WLAN Bluetooth 4.0 (Remove and replace with this one on motherboard)
7. GPU: Zotac GTX 1060
8. Corsair Hydro H70 CPU liquid cooler. (Optional)
9. SSD: Samsung 850 EVO
I have everything working from Handoff, Continuity, Airdrop to iMessage, etc.