Well, if I remember correctly, mod support has been disabled.
Never heard anything of this, although, mods are certainly still capable of being enabled, and you can mod everything else... just not the racial tech trees apparently (unless you directly place them in the Data folder, not the mod folder).
And to be honest, it seems pointless to allow modding of everything BUT the newest feature in TA. If you are going to disable mod support, might as well go all the way, no?
Though, I also like modding, I think it is too early even think about modding TA since it is BETA, which means it is not the final product!
It's never too early to start modding a game!

Heck, I've seen several people mention starting making custom races for their games in TA already, and at least one other person who expressed interest in modifying the Yor in the beta.
I don't want to sound rude, but you shouldn't complain about things not working in beta, its simply not out for modding purpose.
You aren't being rude, it is a valid response. But still, I'm complaining about something that
worked in the last beta, and haven't seen anything stating that modding support was nullifed for this beta and was curious as to what was going on.
Regardless, I have worked around the issue entirely by renaming my Yor tech tree file to "Yor_TechTree2", giving a new internal name, and then putting the RaceConfig.xml file in my assigning the Yor this new tech tree. I will likely release my mod sometime soon'ish.