Would 'Warner Bros' let Gibson anywhere near this?
First off, I'm a huge Mel Gibson fan. I think he gets unfair treatment from the media (and has lost a lot of 'Box-Office' clout, because of such) for simply voicing his opinions (only Spike Lee can get away that....and I think we all know why that is?)
However, I don't think 'Warner Bros' would just hand over the reigns to Gibson, simply because he *wants* to direct it (twenty years ago, perhaps?) but even then it'd likely still be in the hands of Richard Donner.
If it were that easy to star and/or direct a huge franchise movie (like Lethal Weapon) then I doubt Gibson would have taken several (relatively low-budget) DTV releases of recent?
As it stands, it's amazing that he managed to get 'Hacksaw Ridge' released (and to such critical acclaim) but since then, Hollywood has become full-on 'clown-world' (and now the woke Lunatics are running the asylum) Nowadays studios back down to a small minority of butt-hurt tweeters (which is a crying shame)
And to be honest, I'm almost certain that Gibson has burnt bridges with Warner Bros (or vise-versa?) and whilst not completely cancelled, his career now seems (sadly) relegated to that of a supporting roles (for marquee value only)