There are two sides of this I think. One the one hand, yes Elm is an alpha (0.18) in the sense that retrocompatibility is explicitely not taken into account at each new version. This is probably not explicit enough. But on the other hand, it is a very stable alpha since breaking releases happen roughly every year. Plus recently, transitions have been done semi-automatically with the help of tooling.
In any way I think that a team thinking about adopting a relatively new/small language like Elm should first talk to people already on board, either physically at meetups or with the community online (discourse, slack, reddit). And any elm dev with more than 1 release cycle experience could answer these questions. This with the added benefit of having more specific answers, drawbacks, pitfalls and resources references.