Hmmm, well a remake of "Lethal Weapon" means that simply plugging in a mismatched duo doesn't work. Heck people have made jokes including one old 'insert random descriptors' thing on a website years ago that ended "and they fight crime" about the whole mismatched buddy thing. So many shows have done it, either bad or good, that nothing makes this stick out as a concept unless they are going for a literal remake.
To do Lethal Weapon you basically need to have a really deadly guy who acts crazy-goofy at times but is 1" away from suicide (to the point of basically loading guns and staring at them over pictures of dead family members, coming up with increasingly few reasons to not pull the trigger) and another really tough but not quite as deadly guy from a happy, well-adjusted home life, that inevitably becomes his friend and helps him get his life back together, while also acting as the "straight man" for his partner's insanity. Conceptually the whole point is that despite being cops these dudes wind up going waaaay off the reservation largely because of the crazy dude to get bad guys the police otherwise can't handle.
I'll also be blunt, as fun as "Lethal Weapon" is, it's badly timed to do a remake right now even if they found the right guys. Too much controversy in policing with people claiming the cops are actually doing the crap from movies like this without half the justification. I mean let's be honest here, as they even reference themselves, if they were being even remotely realistic these guys would have been off the force so quick it would make your head spin, and none of the in-movie justifications would have likely worked. I mean in today's politically correct age them whacking a dude with Diplomatic Immunity (no matter how justified) could also be seen as more American insanity especially as things are becoming increasingly heated globally.
Most importantly though, I don't think everything needs a remake, reboot, or whatever else. Lethal Weapon and it's sequels were perfect for the time they were made in, and while the last couple of movies were just okay they did touch on the issues of these guys getting old, and how that way of doing things, even in a movie universe, wasn't what it used to be. That was sort of the whole point of the last one.
I've long thought that if someone was going to try and do a violent cop TV show nowadays they should decide to just flat out make "Judge Dredd". Dredd is lethal, and always has a mismatched buddy relationship with his lady partner (classically Hershey or Anderson) who ideally shouldn't be an entire rookie. You don't have to worry about reality intruding too much when dealing with "The Big Meg" since it's pure fantasy, and it can go from being gritty serious to pure satire at the drop of a hat. What's more Karl Urban is apparently employable right now since his own future detective show (which was just okay) called "Almost Human" failed... which was a buddy movie between a human and a robot (and I mean let's face if. if your going to do this, just flat out use Daneel Olivaw).