EXT_disjoint_timer_query could not only be used to launch the GLitch attack, but act as a high-precision timer to carry out Spectre-like attacks
Reducing the timers' precision was sufficient to mitigate the GLitch attack, and as it turns out, Chrome's implementation of EXT_disjoint_timer_query already returned sufficiently lower-precision results.
However, Site Isolation is the long-term defense against Spectre, and it's close to being turned on in Chrome by default. At that point, the EXT_disjoint_timer_query WebGL extension will be turned back on in Chrome.
Other browsers have mitigations in progress for Spectre, and once those land, useful features like EXT_disjoint_timer_query and SharedArrayBuffer will be re-enabled in those browsers, too.