Hello,
I found a blog post on building your own Milight bridge with a ESP8266 and a 2.4ghz transmitter. The original bridge only supports signals for four groups, but with this one you can talk to 260k groups. It also supports the normal Milight API (next to a REST one) so you should be able to use it with the existing binding.
I plan to build one of those in the future. If anyone tries this out please post your experiences!
The Milight protocol he supports is the old one though (V3 bridges) which has only 26 brightness steps and no saturation. As far as I remember there is a firmware emulating a hue bridge for the esp8266. That protocol is a lot more sophisticated.
Especially because the original milight bridges are damn cheap and the effort to build it on your own might not be worth it.
I have this working with a single bulb and mqtt after many hours learning openhab2 the past few days, Works very well so far and I should be rolling it out to control 20+ bulbs when I have time. Confident this is going to work via the mqtt method the hub supports. The way the openhab milight binding is written it restricts the use to 4 groups due to the binding needing a new MAC address per 4 groups and the ESP only has one MAC address and uses ports to expand the groups. Could not get the milight binding going due to that, so moved to mqtt and found it works great.