The closest parallel to the current “Magento 2 might fork” situation I can think of is the SugarCRM/SuiteCRM split.
SugarCRM started life as an open source, self-installed PHP based customer relationship management system. It was one of the many PHP systems that was easy to bucket under the “C.R.U.D. line-of-business application” category.
The needs of the company that controlled the open source project (also named SugarCRM) started to drift away from the needs of the open source community that was using (and in some cases improving) the SugarCRM system. There was a commercial/open-source split, a cloud based/SaaS version of the platform, and the architecture of the entire code base started to change to meet the needs of the commercial aspirations of the SugarCRM company while making life harder for the folks who were just using some free software.
Eventually (in a now deleted forum post from February 2014) SugarCRM announced they had no plans to continue the open source version for the new SugarCRM 7 and four years later fully ended any support for the old SugarCRM 6.5 open source version.
Even before SugarCRM’s blog post (initial commit), a company named SalesAgility had read the writing on the wall and forked SugarCRM as a new project named SuiteCRM. You can read about some the reasoning in a SuiteCRM forum post from that era, but TL;DR; SalesAgility was a company that built out custom CRM systems on top of SugarCRM and wanted to keep doing that. With SugarCRM stepping away from the open source platform SalesAgility forked the project to create SuiteCRM and control their own destiny.
It’s interesting to note that, eight years later, SuiteCRM/SalesAgility itself has enhanced their consulting services with an on demand SuiteCRM hosting service and a product aimed at enterprise users.
Also worth noting, with the caveat that both companies are private and the accuracy of this information might be suspect, is that SugarCRM’s revenue and employee count is roughly an order of magnitude higher than SuiteCRM’s (and that everyone is just grabbing nickels in front of the SalesForce steamroller).
So, forks do happen and the world just sort of moves on.