At the point your text processing utility that was ASCII capably gets a plugin to support UTF-8 or UTF-16 you've made so much of the core modular that it no lon

At the point your text processing utility that was ASCII capably gets a plugin to support UTF-8 or UTF-16 you've made so much of the core modular that it no longer serves the benefit your proposed them for. Replacing core plugins of a program that provide the actual usefulness of it is no better than just upgrading the program. Modularity can be useful, but there's always a core, and sometimes the core needs a change. And that's before we even get into security issues. Sometimes entirely new classes of security problems are discovered, and if they weren't known at the time of writing, how were the authors supposed to guard against them? How much can we fault browsers for not guarding against spectre/meltdown when they were first written and released?