Yep, exactly what i was thinking. Past races showed that RB and Ferrari have issues putting enough heat into the tires. The high temps in Austria actually help them to keep the tires hot, but i suspect the Ferrari will work better on the softs, because the softs got the lowest working range. That might be the reason why the Mercs start on mediums, as the Merc tends to put a lot of heat into the tires. Thus i believe that the merc would overheat the softs. That gives us these strategies, depending on how long the Ferraris can make the softs last:
Merc: medium -> hard
Ferrari: soft -> medium (or hard)
Roumors are that Verstappens contract includes an exit clause if he doesn't reach a certain position in the championchip. He's currently 4th, so IF this clause exists, it must be "3rd or better". However that's a rumour. We don't know if such a clause exist and the date when it applies (if it exists).