Jared said somewhere that if he was vehicle lead when the Sunburst was initially being developed he would've put a boxer in it. There hasn't been any confirmaion that this change will happen though
No, I imagine it's as simple as Gabe just didn't want the Sunburst to have a boxer engine. IIRC Gabe mentioned that the Sunburst was mechanically based on the Evo anyway... Nowadays Jared is lead on vehicle team and owns a contemporary Subaru. But he also might not want to make a major change like that to a car that was in game before he joined the team; and we're basing all of this on a single passing comment he made years ago that he probably forgot about....
Ok this reminds me Someone down the road has both a newer WRX and an older WRX, in the exact same color
It wouldn't make sense for there to be a factory I block and H block both in the same platform. In Subarus it's rare to even see a different block type swapped in