i am not able to use elgg 2.x yet on my live site because of the lack of stable/TESTED code for it in the form of plugins (including my own) and possibly in some of the core aspects too. whereas even elgg 1.12.x is pretty well tested, stable and supported at present. therefore, i think/feel it is a bit misleading to call 2.x the stable version, since that isn't really what it is and new users may install 2.x and then discover they can't use a lot of the plugins they need because there aren't stable versions of them yet.

if i were to name the two branches, i might go with 'cutting edge' for 2.x and 'stable / LTS' for 1.12.x.

just my two bits ;)