Is There a RTR Equivalent for MTW?

Is there a mod along the lines of the Total Realism mod (i.e. 100% historical accuracy) for MTW/VI?

Not 100% historical accuracy. However, you can try the XL Mod or the SuperMod for more historical accuracy and a much better gaming experience.

They both have improved maps, more units, more factions, etc.

XL Mod has a tighter economic system, so you can't earn infinite florins through trade. The factions are nicely balanced. Glorious Achievement points work. The AI builds armies better. Overall, it ends up being a better and tougher game.

SuperMod has three new maps (one for each period). LOTS of new units. New buildings. Lots of new factions. There is a lot of easy money so development and troop building can be done without difficulty. It ends up feeling very different from XL because of the different economic systems.

If I were you, I'd try them both. They both have a lot to offer, and personal preference has a lot to do with which one people like better.

While not aimed to 100% realism i'm also working on a MOD that gives more characterization to the various factions using MTW + VI units.
Now mercenaries plays an important role, especially on early as you have to compensate for your roster shortcomings (eg. Danes lacks heavy cavalry).
I found XL a bit plain as the variation offered doesn't really add much difference.
It's not criticism toward the MOD in itself, but you can modify units only so much so imho role specialization works more than having dozens of different rosters that do the same stuff under different names.