Once per period, all of Archie's constituents are surveyed to determine if they still like what he's doing. They can change registration at any time, but this is the most convenient time to do it.
If Archie drops below 1M at any time, he goes back to one vote. If he drops below 500K at a survey point, he's no longer a Representative.
So i realise why I like aspects of your proposal. Because it has a few of the principles of the Mixed-Member proportional  System mixed into it. I like MMP I really like it. I think that combined with a radical expansion of the number of representatives ( I think we should be closer to 100k then 500k, maybe as low as 50k ) would allow us to do many amazing things as a country. Also I would toss this wrinkle in. MMP is done at a state level and only state level political parties are recognized, and they are now official. They must follow rules to elect their leadership.