Teribus
I was part of a very small team entrusted with Western Europe's Article 5 commitment for ten years 2001-2011, and as a senior officer in a larger team for 8 years before that, 1993-2001: my late spouse was central to that team for five years before that. Article 5 is not meant to be a hair-trigger in the way you describe, but as a bottom-line buck-stops-here defence of the survival of a nation.
If it were invoked in the way you describe, it would be devalued. Politics and international relations requires a certain robustness, and during the Cold War, the Eastern Block was forever perpetrating minor incursions along the Iron Curtain border. These were on the same scale as may be envisaged from IS, and so i see no reason whatsoever for the Article to be invoked, not least because IS is amorphous and cannot therefore be treated with.
The existing provisions for response to terrorism are entirely adequate for any measures needed. The bombing is not undertaken in the Article 5 framework, for example, and it moreover demonstrates the Russian position on Syria is not as you describe: they have changed radically over the last month, as they are likely to be on the receiving end of whichever body wins in the IS vs Kurds battle, and so the vetos flung around with wild abandon in the UNSC a year ago are now strangely absent. Kurdistan also includes a chunk of Southern Russia, and IS aligning with the Chechens is an even worse nightmare to them, as they might suck in the rest of Muslim Central Asia.
Russia's support for Syria was never altruistic, as I've described here previously, but in defence of an interest in the Med ports. However, Syria no longer controls them, IS have cut them off from Damascus, and so Russia is less interested in Assad, whose past human rights record comes home to roost. Had Assad not provoked civil war, none of what has followed would have happened, and Russia will also ask him for its price.