Well, everything works flawless under 10.13 SU with the ASUS Prime X299 Deluxe and the i9-7980XE, as long I do not enable the multi core enhancement BIOS feature. With the latter BIOS feature enabled, my system would reboot just a few moments after login. However, under 10.12.6 there are absolutely no issues even with the multi core enhancement enabled and the Geekbench score boost is tremendous, i.e. 51.000 (disabled) vs. 58.000 (enabled)! Nevertheless, with the i7-7800X, I could use the multi core enhancement also under 10.13 even before SU. Give time to the mainboard developers and also to Apple to fix remaining issues.
In any case, with the multi-core enhancement disabled, your system should work flawless and absolutely stable... If you still face reboots, something else might go wrong... The reason might be one of the 10.13 beta versions your are still using, but I doubt that the latter is really the cause.... Although within this beta version you will not have for e.g. native XHC USB support in any case. Thus a board-specific XHC USB Kext might still be mandatory for XHC USB2.0 and 3.0 functionality.
Also the Skylake-X and XCPM support dramatically improved within 10.13 SU for many Skylake-X processors. E.g., the i9-7900 or the i7-7820X do not require anymore any kind of aml stepping, everything is already natively implemented.
I am indeed very happy with the ASUS Prime X299 Deluxe...
I think we can be proud and totally satisfied with what we reached so far! At least my build behaves absolutely stable and works flawless with respect to my personal requirements and expectations. I still would like to improve some minor issues, the multi-core enhancement functionality with the i9-7980XE under 10.13 would be one of those... Full sleep/wake functionality also with the TB EX 3 is another thing I am currently aiming at and latest results are indeed very promising.