Via Bungie's Weekly Update:

''In closing this week, Bungie would like to give an official shout-out to the fine men and women at High Moon Studios. For a while now, we’ve kept our love secret, but it has become known that they’re working with us. Please join us in welcoming them to the party!''

Source: https://www.bungie.net/en/News/News?aid=12965

Some of High Moon Studios' previous work:

Darkwatch (2005) for the PlayStation 2 and Xbox
Robert Ludlum's The Bourne Conspiracy (2008) for the PlayStation 3 and Xbox 360
Transformers: War for Cybertron (2010) for the PlayStation 3, Xbox 360 and Windows
Transformers: Dark of the Moon (2011) for the PlayStation 3 and Xbox 360
Transformers: War for Cybertron (2012) for the PlayStation 3, Xbox 360 and Windows
Deadpool (2013) for the PlayStation 3, Xbox 360 and Windows
Call of Duty: Advanced Warfare (2014) for the PlayStation 3 and Xbox 360

Source: http://en.wikipedia.org/wiki/High_Moon_Studios#Games

If I'm not mistaken by this language, this means that High Moon Studios will be assisting Bungie on future Destiny content; whether it be expasisons or a full fledged sequal. This also means they were not involved with any content released so far, but will be involved with upcoming content. 

Am I reading this correctly? If so, they will need all the help they can get with gaining consumer confidence in the Destiny brand. Good luck to them...

And another studio downgraded to dlc/ports

Actually, I think this is a good thing for the studio. Working a project of high priority is a good stepping stone for them. If their work turns out to be deemed worthy by Activision, they may be given larger projects. Going from a movie tie-in, to a comic tie-in, to a port of their most successful franchise is progression. Activision must recognize that High Moon Studios can handle projects of larger significance, thus they moved them to asssit Bungie with Destiny. Considering the issues associated with that franchise, getting as much talent to bring content to the series is very important.

This move most likely means we will be seing a Destiny 2 earlier than inidially expected, that or more expansions.

That already happened to them last year.