We have not heard anything much lately about the NVIDIA SHIELD Tablet. The last one we noted was the Nougat OS rolling out to several devices from the company. That was almost a year ago. The brand has already released similar updates for other devices including Nintendo Wii games for the NVIDIA SHIELD TV in China, SHIELD Experience Upgrade 6.2, and YouTube TV for the SHIELD TV. Not all NVIDIA SHIELD products may receive Oreo but Security Bulletins should still be released regularly.
The latest Security Bulletin for the NVIDIA SHIELD Tablet includes security updates for those CPU Speculative Side-Channel Vulnerabilities aka Meltdown and Spectre. The issue was discovered earlier this month. NVIDIA is one of the few that has responded to the reported security issue. NVIDIA believes the SHIELD Tablet is immune to the problem and so a proper update must be applied to reduce possible exploitations.
The Google Project Zero disclosure lists three variants of the vulnerabilities: Variant 1 (CVE-2017-5753), Variant 2 (CVE-2017-5715), and Variant 3 (CVE-2017-5754)/Variant 3a. (More information available HERE)
Check manually if updates for the NVIDIA SHIELD Tablet are available. Head on to Settings > About > System update. You should see either of the following: 1.0 (January 4, 2018/Initial release) or 2.0 (January 16, 2018/Clarified affected Arm CPU components).