Not at all. Look at the rankings breakdown of low top 10 players. Even at 40 Federer will be able to do that easily. I'd go as far as saying that Federer's year of WTF qualification depend solely on his health and motivation, he's far too good to stop being a top player before he calls it a day.
I have had the same thought for a while now but I have called myself delusional and thought others would do the same. I mean Agassi was top 10 shortly before he retired (he was barely playing by the time he was 35) and that was a stronger era as well. If Federer can avoid injuries, he can definitely stay in the top 10 until he's 40.
Whether he'll have the motivation and desire to do it is a separate issue though.
I just saw this on Twitter.
Is Fed trolling his fans
Originally Posted by rene stauffer @staffsky
#Federer still undecided about a start in #Shanghai. Might decide as late as next week if he will travel to China, i heard.