fallback_sti_to_base.rb

# FallbackStiToBase
#
# This concern provides a customizable fallback mechanism for Single Table Inheritance (STI) in Rails.
# It allows specifying which types should raise an error when not found, while others fallback to the base class.
#
# Usage:
#   class Action < ApplicationRecord
#     include FallbackStiToBase
#     validates :type, presence: true, inclusion: { in: %w[Value1 Value2 Value3] }
#     fallback_excluded_types 'RemovedValue1', 'RemovedValue2'
#   end
#
# Benefits:
# 1. Prevents errors for missing subclasses by falling back to the base class.
# 2. Raises errors for specified removed subclasses to avoid potential issues.
# 3. Allows for additional validation or behavior in the base class.
module FallbackStiToBase
  extend ActiveSupport::Concern

  class_methods do
    def fallback_excluded_types(*types)
      @fallback_excluded_types = types.map(&:to_s)
    end

    def sti_class_for(type_name)
      type_name.constantize
    rescue NameError
      if @fallback_excluded_types&.include?(type_name)
        raise
      else
        self
      end
    end
  end
end

Upd: published a Gem: https://github.com/osbre/sti_fallback