If someone tells you they have a plan for a minority (< 50%, by definition) hardfork of Bitcoin using an existing unmodified client, then you should be a little skeptical. Perhaps they have forgotten about difficulty.

Any current unmodified client will respect the rules that the valid chain with the most work is the active chain.

Unmodified clients should not accept chains with sudden difficulty resets in them.

A miner who thinks they can mine a spin-off chain until it exceeds the length of the active chain must have a lot of hashpower, or they might be thinking of advance-mining that chain under tweaked (non-real-time) clock conditions.

Why I am posting something which seems so obvious?

Well, because sometimes the obvious tends to be forgotten or not mentioned on purpose...

Any minority fork attempt should give ample advance notice and clear information so that fair mining can take place on the spin-off chain. Let's keep this in mind.

As far as /r/btcfork is concerned, we will not endorse spin-off attempts that violate such basic premises of fairness in mining.

To those who would say "but SHA256 mining is not a fair environment anyway", I would just say that a minority spin-off should not make a bad situation worse.

Otherwise we risk damaging the reputation of Bitcoin.

P.S. This post is not to be confused with ViaBTC's plan to upgrade via a majority fork using BU. I think that would be feasible, if done with a large majority (~75%).