PG13 wouldn't surprise me, just the way it seems to be at the moment, where they think they can expand ticket sales.
Just looked at Expendables as I didn't see them all but here they went from 18 to 15 to 12. I'd be worried about 4
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Cubed, re your comment, I'm not sure it was the case of knowing when to quit at the point of the 3rd movie, they could have just made a better movie
At this point though it's different, but I still like the franchise (not every movie was great) so will still want to see it.
If they are planning to spread out over 3 movies but quit if the first one fails, I don't want it ending on a cliffhanger, hopefully they will write it so that it can be it's own thing given they know it could fail.