This reminds me, I still have unreleased teensy code for driving WS2812. Interest never seemed high enough to warrant a realease, especially because it does not use DMX at all, but a better fitted network structure (8x32led chunks, no universes, just IPs).
Anyhow, with it I can stream rgb data for 4k individual LED at 60Hz over Ethernet.
And because the UDP nodes are much better then the RS232, use of more than one controller is easy.
Because the data is prepared within vvvv, it is possible to "record" to a binary file with the Writer node, and copy the file to a SD disc. If inserted to the Teensy, it will playback those files, in case the ethernet stream breaks up.
So yeah, Teensy!
But I guess an honest answer boils down to something like this:
If you have a weak spot for putting custom code on your device, or extend it arduino style with sensors and crazy shields, and pushing the hardware to the limit, Teensy is your friend. If you hate soldering and coding C, and are already worried when having to update your devices firmware, then ready-made Enttec et al are your better bet.