"In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work." -17 U.S. Code § 102 (B)
Under US Copyright law it is entirely legal to make an open clone of Games Workshop's rules.
If people are tired of GW bullshit about "Counts As" and retiring old units and stuff then JUST FORK THE RULES and start playing that instead, with community iterations of the point values. Hell, there could even be points values for Warmahordes and Star Wars Legion.
You don't need a company to keep a game going. SWCCG tournaments lived for decades after Decipher abandoned it. What you need is just a critical mass of people who play it to give the rule set enough momentum to be worth having tournaments. If an open, community managed wargame caught on, it would take the wind out of GW, who have been extremely poor stewards of their game.
That's what I've done. I play a 40k based game with a set of additional and variant rules of my own devising.
Ultimately taking what I like and eliminating what I don't.
It's... playable with official units, but a great deal of it relies on our own custom factions. I don't mean to say it's not balanced against official, I mean that there's a few stats that work differently and would need converting. But it isn't hard to do.
The upshot is that we can hotfix whatever we like, the ruleset is devoid of bullshit because we kill it, and the game is by and large better in my opinion.