>> [2. text/x-diff; 0002-Add-command-to-start-Emacs-with-specific-packages.patch]...
>>
>> [3. text/x-diff; 0001-Add-a-function-to-query-the-Emacs-executable.patch]...

I have slightly modified your version, fixing issues I had, in case
anyone else wants to try it out:

        (defun package-isolate (packages)
          "Start an uncustomised Emacs and only load a set of PACKAGES."
          (interactive
           (list (mapcar #'intern (completing-read-multiple "Packages: " (mapcar #'car (package--alist))))))
          (let* ((name (concat "package-isolate-" (mapconcat #'symbol-name packages ",")))
                 (deps (mapcan #'package--dependencies packages)))
            (apply #'start-process (concat "*" name "*") nil
                   (list (file-truename (expand-file-name invocation-name invocation-directory))
                         "--quick" "--debug-init"
                         (format "--eval=%S"
                                 `(progn
                                    (require 'warnings)
                                    (add-to-list 'warning-suppress-log-types 'initialization)
                                    (require 'package)
                                    (setq package-load-list
                                          ',(mapcar (lambda (p) (list p t)) (append packages deps)))
                                    (package-initialize)))))))