Two enemies from the 2002 game for Nintendo GameCube.
On November 03, 2017, Nintendo of America Inc. filed a first request for extension of time to file a Statement of Use for its trademark application US Serial Number 87274495, Eternal Darkness, originally filed December 20, 2016. The request has been granted. A Notice of Allowance for this application was issued on May 09, 2017. An SOU may not be filed more than thirty-six (36) months from when the NOA issued.
Source: http://tsdr.uspto.gov/documentviewer?caseId=sn87274495&docId=ESU20171104160913#docIndex=0&page=1
The story of the Eternal Darkness trademark is quite long (in the US anyway), so far four applications have been filed (and three of them abandoned after time):
As you can see, this practice is nothing new and as far as I have been able to collect Nintendo can keep doing this indefinitely as long as they keep paying the fees.US Serial Number 75672853, Eternal Darkness
Filing date: April 1, 1999
Abandonment date: December 19, 2009 (Registration cancelled because registrant did not file an acceptable declaration under Section 8)
US Serial Number 77932350, Eternal Darkness
Filing date: February 10, 2010
Abandonment date: August 19, 2013 (Abandoned because no Statement of Use or Extension Request timely filed after Notice of Allowance was issued)
US Serial Number 86017853, Eternal Darkness
Filing date: July 23, 2013
Abandonment date: February 6, 2017 (Abandoned because no Statement of Use or Extension Request timely filed after Notice of Allowance was issued.)
Active US Serial Number 87274495, Eternal Darkness
Filing date: December 20, 2016
What Nintendo is doing with this IP we can only speculate about, but in prior filings the ongoing effort says "product or service research or development". This could mean they are researching or developing a new, original Eternal Darkness game, an HD remake or a version for Virtual Console. It could also be a simple control measure to try and prevent another party from using the name Eternal Darkness (for game software or something else). We'll see what happens in due time, but I have to say it has been a long journey with this mark.