This news follows a long period of downtime, rampant spam attacks and inactivity across the boards. Moving to Magento SE signals that Magento, Inc has faith in the maturity of Magento SE even though it is currently still labeled as beta.
Founded early 2013, the Magento StackExchange hosts an average of 34 questions per day. A rough 80% of them get answered and more than 200 users are actively contributing to the Q&A platform. Notable contributors include Marius Strajeru and Fabian Blechschmidt.
The Magento forums will stay in maintenance mode until June the 19th, after which it will be put back online but in read only mode. This will be the signal for collecting and migrating all useful topics to a more permanent and indexable place: the Magento forums host a wild variety of gems accumulated over the years. For those currently looking for that obscure topic from 2008 on some undocumented core feature, Google its cache or the Wayback Machine might be of help.
Question remains is whether Magento SE is able to replace the old forums completely. Though it is indeed proving to become an invaluable resource, it is still very developer oriented whereas the forums were also hosting a variety of user-centric content. Time will tell.