I think he wants a shot at the governor's office. The Senate seems to cramp his style, and he doesn't have the chops for national politics. He was Lt Gov, and has a significant advantage in name recognition and fundraising as a current Senator. Plus, the DNC is probably already vetting primary challengers to run against him in 2030.
PA is a weird state, in every way possible, and Shapiro did a lot of damage to his image in his attempt to land the VP job. If Shapiro decides not to run for reelection, the Democrats don't have a deep bench in Pennsylvania. Austin Davis is probably the only other name worth considering.
Fetterman would not win anything in a nationwide race, but if he can bring the Pennsyltuckians out to vote for a Democrat, he would win the state in a landslide.
the DNC is probably already vetting primary challengers to run against him in 2030.
Why would they? What has he done to anger them? If anything, having another Sinoma/Manchin waiting in the wings gives them more excuses why they can't do the things their constituents want them to do.
The ideal position for the democrats is controlling all 3 branches, but being unable to actually do anything their constituents want, since the desires of their constituents are mutually exclusive with those of the donor class.