Whether this proposed change is worth a PEP is a value judgement, but 
whether it will need a PEP is, I think, a fact. It is a backwards 
incompatible change (it will change the inheritance order of classes) 
potentially breaking people's code. Its not a small change, so it will 
(almost certainly) need a PEP.

The C3 linearisation algoritm has been published in the academic 
literature, where it has been peer-reviewed. It has been in use in 
languages such as Dylan, Python and Perl 6 for at least 16 years. Your 
variant is experimental and untested (unless you can point to languages 
already using it). It won't be easy to convince the core devs to change 
algorithms unless you can point to an actual problem with the status quo 
more serious than "it surprises me".

I don't think the bug tracker is the right place to debate your variant: 
probably not enough eyes on it, and I'm certainly not qualified to pick 
out problems with your design or judge if it is better. If you want to 
take this further, I suggest you try the Python-Ideas or Python-Dev 
mailing lists:

* Python-Ideas is high-volume and plagued by bike-shedding, but is the 
official first step for proposing major changes to the language.

* Python-Dev is lower volume and more likely to catch the eye of senior 
core developers, but they may tell you to take it to Python-Ideas first 
(but not always).

https://www.python.org/community/lists/

If you don't like mailing lists, you could try Discuss:

https://discuss.python.org

Whichever forum you pick, be prepared for serious push-back. The onus 
will be on you to prove that the status quo is not good and your 
alternative solves some real problems. You might want to read these 
first:

https://www.curiousefficiency.org/posts/2011/02/status-quo-wins-stalemate.html

https://www.curiousefficiency.org/posts/2011/04/musings-on-culture-of-python-dev.html

I'm telling you this not to discourage you from taking it further, but 
so that you understand that if you want this change you have to be 
prepared to work for it.

Good luck!