That's a nice thought, to have different scales to look at, maybe even a separate tank window with larger more clear numbers, like an "average tps" and "current TPS" entries.
Personally, TPS is a little murky. The reality is that threat IS spikey, regardless of class/spec, and it isn't worth getting too concerned with specifics. I, too, like to keep a close eye to see what my best spikes are, what my minimum cruising value is, and keep rough track of my threat profile over fights for the sake of refining spec/gear/priorities and the like, but I think it all needs to be with a heavy grain of salt. The real concern with threat is that you can keep your total above anyone on the dps, right? Well, technically you even have a margin on that, but with the in-game meter and the way they all read now that isn't represented. Really what you're looking for is two distinct threat abilities: initial threat and longterm threat. You want to know that you can either build faster or burst ahead in the first 5-10 seconds of a fight, and then that you can continually generate at least as much threat as the rest of the raid through the remainder of the fight (ideally more than, few people ride razor's edge, and it is increasingly stressful the closer you are to it).
I think the best you can hope for is a rough sense of values, and really, if your dps section can't touch your threat, then nitpicking over little changes isn't going to do much for you.