I do not claim to speak for Pat, but as a Slackware user for some years I can say that I like the conservative approach that Pat takes to patching upstream code. To me, the people who write and maintain the upstream code are those in the best position to judge whether a patch should be accepted. If patches are accepted from third parties, then it adds additional complexity to maintenance and support. For an example of this see http://fixunix.com/ppp/62413-unrecog...aultroute.html
If you want to see this patch in official Slackware, then it would be better to lobby the official pppd maintainers to have the patch accepted into the upstream source.