I think apple will certainly add an Iris Pro version of the to the 15 rMBP lineup.
The only reason to want a now 750m is for gaming as the Iris Pro is already much better then the 650m/750m on GPU compute. (if you don't need cus
I can see them doing 2 versions of the 15 inch rmbp this year and drop the Classic 15 inch. Cheaper one with Iris Pro and a more expensive one with 750/760m. And then next year go intel only, because the next generation Iris pro (at 14nm) will be faster than the 750m. I highly doubt we will see a 765m because of this reason and of-course thermal reasons.
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100% agreed

It will also come at a lower price!