Mainline-based LE also works on Odroid-N2 and it was ready earlier than for VIM3 simply because the Odroid was ready earlier.
It is a work in progress but support for both boards should be almost equal in mainline-based builds. I also think that CE support is a matter of creating a device tree for VIM3 and like you said: most of work for S922X was already done for N2 and every S922X can reuse it.
Is hw decoding working on the N2 with mainline?
And how about hdmi audio and ethernet?