Is selfish mining still an option with compact blocks and FIBRE?
While FIBRE has done an incredible job in reducing relay times for blocks which are new, many miners additionally have systems by which they relay their own blocks in a single packet and have them queued up to relay on when they start mining the template, not when they find the block. Ultimately, FIBRE's few milliseconds of delay will lose to a single UDP packet that just relays the winning nonce around. Further, selfish mining attacks are very non-linear in the advantage you gain from a relay advantage - if you're 1ms faster to most hashpower, you have an advantage to that hashpower, period.