OpenWrt 18.06 is technically just the next version after LEDE 17.01 (which was, technically, just the next version after OpenWrt 15.05).
Only on a organizational level, there were different opinions and goals within the project that caused development to continue under the LEDE name for a while.
So I very much expect that a (hopefully near) future version of the Omega2 firmware will be based on OpenWrt 18.06.
In fact, a stock build of OpenWrt 18.06 works fine on the Omega2, incuding usable WiFi via the opensource mt76 wifi driver. Most user-space Onion additions will probably work with no changes (omega2-ctrl for example is fine), some Onion specifc kernel modules might need small adjustments in the opensourced code. However, the proprietary wifi driver needs to be updated for the newer kernel by Onion themselves.