Getting the people I e-mail with most to use PGP encryption with me would probably require 20 minutes to 5 hours, probably in person, with each of them. That is likely more time than people spend on professional dental care annually and, if I'm doing the setup, I have to spend that time with each correspondent.
Getting them to also use some kind of homegrown obfuscator or custom block cipher with me (but not with their other correspondents?) is another effort of several hours per person, again requiring meeting in person with each correspondent.
Both of these mechanisms are then very fragile if a given correspondent changes devices or operating systems.
You might argue that, for each person, learning how to use a tool like GPG is on par with getting annual dental checkups (possibly annoying and time-consuming, but just a few hours, and with potential hard-to-foresee benefits over the long term). And that's fine, but if we're still talking about adding completely homegrown custom layers intended to defeat automated cryptanalysis, the picture has gotten a lot more complex. By definition, the people adopting these solutions have to design and deploy them in a customized, personalized way, to avoid having large populations of people adopting the same tools and techniques. If this is supposed to be reliable (and somehow coexist with other custom techniques, so that Alice and Bob can use one homegrown obfuscation layer while Bob and Carol use a completely different one!), I expect it would be an order of magnitude more effort even supposing that most of the participants are already capable software developers.
I mean, maybe there's a way to extend OpenPGP so that you declare a "custom cipher" on top of the main ciphersuite and then implement it as a plugin so you "just" have to do the core work on your custom thing and not on the surrounding key exchange mechanisms, data format, and e-mail client integration... but it still represents a massive amount of additional work for each pair or small group of communicating parties, even given this hypothetical infrastructure.