Russia nor novorussian rebels had nothing to gain from this shooting - except for political disaster for themselves. On the other hand, Kiev government had a lot to gain. First I describe current situation because for some strange reason there is nothing about this in western mainstream media.
In the last few days rebels managed to do a heavy spanking to ukrainian army and national guard (ie. right sector). Large number of their soldiers (approx 3-6 thousands, 10% of army!) have been trapped in a cauldron north of Saur Mogila, between Doneck/Lugansk and russian border without supply, being constantly shelled by rebels: entire batallion has been nearly wiped out (72th or 79th), 24th battalion has also been decimated. Lots of those soldiers dropped weapons and uniforms and tried to escape to Russia. In Lugansk airport at least two ellite groups are trapped, Ukies tried to establish corridor to get them out but their column suffered heavy losses - some of them managed to get to the airport but they failed to keep up corridor open, so they're trapped there as well. Rebels are constantly pounding them with mortars and artillery. Between 9th and 15th july, according to Ukie defence ministry they had more than 1500 soldiers killed in action, more than 4500 wounded, lost almost 40 tanks and more than 100 trucks plus several planes (they were losing approx. 2 planes a day over several days). Ukies started retreating and begain fortifying outside Lugansk/Doneck oblasts. To sum it up, they've suffered catastrofic losses, almost strategic defeat. There are suspicions that Kiev govt now fears that their military can turn against them, align with rebels, mop up right sector and national guard and overthrow Poroshenko government.
Losing badly, Kiev desperately needs something that would change the course. Direct NATO intervention would be ideal for them, if not then at least some ceasfire, so they can regroup and go on with some new plan. Shooting down civilian plane with 300 passengers and blame rebels and Russia for this plays ideally into their hand. Having said that, I strongly suspect that Kiev government is behind this tragedy - if not shooting directly, then indirectly by directing this plane into territory where military action is going on.