I think the final episode won't have any twists to be honest. I think it'll be fairly straightforward; Osborne will be H which will tie neatly back to S1E1 where Steve was forced out of his glamorous role to join AC12 because of Osborne's cover-up of the shooting. After being set up as "H", breaking his back, his pain now and painkiller addiction, he'll be vindicated at last. Was it worth it though...?
The only "twist" will be that Steve won't dob in Ted for telling Lee Banks about the rat and giving the proceeds of crime money to Chicken Licken, so they will both end up being less than truthful, verging on corrupt (but we like them so that's alright... does that make us corrupt too...?).
The tension will come with knowing the clock is ticking on Steve's suspension (I think perhaps Ted's retirement doesn't fit into the timescales of this episode but may be covered in the flash forwards that the series always end with).
That really only leaves Thurwell's involvement. I think over the whole story arc, it doesn't matter if Jo lives or dies.
I think the recent watchers will be disappointed by the lack of action but it'll reward those who've watched over the last 9(?) years.
I've probably forgotten something crucial and there will be fireworks.
Also conscious I've ignored Kate mate, but from this hypothesis, the story is all about Steve vs Osborne.