If you're going to do another one then make it a role reversal. Have a Nakotomi style situation with somebody else in the building but have McClaine be on the outside talking to that someone. Basically he becomes the Powell character from the first film. This is the only way to make it fresh. Now, with that said, who would you like to be the "McClaine" in that story?
So in that case, I guess it's like handing the reigns of the series over from McClane to somebody else (even if it's just for one final film). If anybody were to become the McClane of that story, I'd hope that it's not Jack McClane. I did not like his character one bit, or the actor.
The original trilogy was brilliant, the first is easily up there with one of the all-time greats of the action genre (only T2 Judgement Day tops it, imo). Hell, I even enjoyed the fourth movie for what is was because in spite of it's inconsistencies with previous films, it at least had some good action scenes and some old-school McClane wisecracks.
The fifth movie however was absolute sh*t. The ugly visual style and incoherent action scenes were bad enough, but then you had a bunch of forgettable villains and worst of all, that insufferable little c*nt Jack who does nothing but whinge and moan at this dad (despite how many times John saves his arse). To be honest, I knew it was DOA once I found out they'd hired the director of that crap Max Payne film. After that trainwreck, I really don't have any hopes for a sixth film. A prequel especially sounds like a terrible idea and if anything would just screw with the original. What would even be worth showing in McClane's life before his night at Nakatomi Plaza?
If anything, they should at least bring back Sgt. Powell. He was only in the second film for a brief moment and we haven't seen or known what's become of him since.
Die Hard 1 is absolutely among one of the greatest action movies ever, I think I preferred the third film as my personal favorite in the series but there's no denying that 1 is still amazing. Even 2 wasn't a bad film for a sequel, but it wasn't as direct of a sequel as 'With a Vengeance.' I actually didn't like 4 that much when I first saw it in theaters, but I ended up getting the DVD for Christmas later that year and the movie grew on me. It wasn't a bad entry to the series, but it still wasn't the best one. If that had been the last film, it would have been fine.
A lot of the villains in 5 just seemed like random stock action movie villains. There was nothing truly memorable about them, I thought the singing cab driver was a more memorable character than them. Jack was a terrible character, as well. Plus, there was a load of random stuff that I just found to be annoying. Like McClane driving over people's cars and probably hurting or killing a bunch of innocent people, or the fact that the filmmakers evidently forgot that Chernobyl is not in Russia, yet they managed to make it there in record time and cross the Russia/Ukraine border with a car full of guns. And then the fact that some magic spray apparently reduces radiation, and John McClane is impervious to radiation poisoning and massive falls. I know it's an action movie and you obviously have to have some suspension of disbelief, but the original Die Hard films did not have nearly this many complete lapses in logic and near-invincibility of the protagonists (plus, I really can't help but nitpick when it's a sh*tty movie).
I don't think there'd be much reason at all to show McClane's life before the Nakatomi incident, and if it turned out that he fought off some terrorists or even really experienced bank robbers/mafia before that film all single-handedly, then it'd kind of make the importance of what happened at Nakatomi Plaza irrelevant since fighting a bunch of crazy guys on his own would be like no big deal to him by that point (and on top of that, unless they can find someone who looks almost exactly like Bruce Willis, then McClane's appearance would have also changed drastically in about a decade and he'd look like a completely different guy). But I always wondered whatever happened to Powell. I guess you could say that after transferring back to NY and going into his alcoholism, McClane either hardly ever spoke to him anymore or just completely lost contact with him. A reference or a small appearance in the fourth film would have been a nice touch though.