It's strange, but Kipchoge's reputation had taken a huge hit in recent months, especially considering that he broke the world record (with a huge positive split, no less) just last fall.
There are three obvious reasons for this:
1) His age. We keep waiting for it to catch up to him, and it never did; maybe now it finally has
2) His Boston performance, which was perhaps his worst marathon. Of course, after his other "worst marathon" he bounced right back to win Olympic gold and break the world record
3) Kiptum. His London race was nearly the mirror image of Kipchoge's Berlin World Record. He seems like the next big thing.
With an athlete like Kipchoge, we're always looking for the beginning of the end, and perhaps Boston was it. Maybe he'll underwhelm in Berlin this weekend, race poorly at the Olympics (or even miss the team), and never return to the form he's been in for the past several years. It's certainly possible.
Or maybe Kipchoge hasn't lost a step, he once again dominates in Berlin, maybe Kiptum has already run his best races (the vast majority of elite marathoners have a very short time at the top). Kipchoge could win Berlin, win Tokyo (or whatever), and then three-peat next summer, with Kiptum nowhere to be found.
On some level, all of this is obvious, but I bring it up because I think whatever happens will seem obvious in retrospect, but right now wildly divergent outcomes are possible.