I see I am late to the party. Time zones being what they are and all.
While it would seem we are speculating some on the incident, the speculation is on a solid foundation.
The 737 has an excellent safety record. It is actually not super rare for a engine to "explode". I am no jet engine expert but the main fan at the front of the engine is normally what comes apart I believe.
We have been flying for over 100 years, we pretty much have it figured out. Such incidents are planned for. I believe last year there were 3 reports of fans "exploding" with one fatality (lady who got sucked out a broken window). All the planes landed safely.
Here I give you a list of commercial airliners who have been shot down by a military entity.
en.m.wikipedia.org
It happens more than most think. I would focus on 3 incidents in general
KAL 007, shot down in 1983 by the Russians at the height of the cold war.
Iran flight 655 shot down by USA in the Persian gulf.
(Actually were quite a few in the '80s, 2 in just a couple month in Afghanistan)
And Malaysia flight 17 over Ukraine.
Fact is, during hostile times people get itchy trigger fingers.
So far the evidence, circumstantial or other wise points to Iran shooting the plan down. Probably accidentally.