It was known by Intel, AMD, Google Project Zero, and a few others during the multiparty responsible disclosure process, which took a couple of months. There's some speculation that Intel's CEO made his recent share divestment decision based on the disclosure timeline.
Now that it has been disclosed I fully expect others to focus on more microarchitectural vulnerability research on x86, ARM, and other architectures. I think a lot of this was spurred by recent developments in cache side-channel attacks, so we're likely to see a repeat pattern.
Of course we're also likely to see refinement of the current exploitation approaches too. These attacks will continue to get better and will probably adapt to work around the latest updates to Intel's microcode, and new kernel patches.
The best part for us is that it'll finally force Intel/AMD to take cache side-channels seriously and implement proper defences (e.g. cache line indexing keyed against privilege levels, or fully isolated kernel/usermode caching) in new silicon. Although that'll be a year away.
