Well, IntelliJ often uses (special) dev releases directly from the main branch, like 2.4.0 in 2026.1 EAP, so as a plugin author, you need to update your plugin very often/fast, while also maintaining support for other IDEA versions. If the feature will be enabled by default, the FIR api should be more stable to reduce the work for plugin authors.
Or introduce a mechanism (like Gradle attributes) to select a different version of the plugin for IDEA only.