This development certainly shifts the power of influence as far as sports broadcasting is concerned, to ABS-CBN. There have also been earlier reports that the NBA games will now also be on Studio 23. So the three most popular leagues in the country will now be on Studio 23, the UAAP, the NBA, and the PBA. This puts ABS-CBN sports as a clear leader in sports broadcasting in the country. I reckon Solar probably did not like the way things were going and needed a change of scenery to right the ship, thus the partnership.
Solar is no stranger to reformatting. They've reformatted RPN 9 a number of times. At the beginning of this year, they announced that ETC and Solar TV are both going to get major facelifts. So this new direction now does not have room for sports.
Hey, just as long as we all still get to watch high quality sports programming, the networks can do whatever they want.