IS bomb on Russia plane would herald new phase in conflict

You are not a secret service agent then.......?

Plausibly deniable. I fear this may be a triumph for ISIL counter-intelligence. Plant disinformation for the Western security services to uncover to show it was an ISIL bomb, and thereby destroy the Egyptian tourist industry. If the Egyptian accident investigation report says it was probably not a bomb, it is likely to be regarded as another whitewash like the official report on Egypt Air 990 not being pilot suicide.