
Now it is apparent that the Rating Points you have at the start of the week will decay, and if you do not pvp you will lose rating and ranks. Some people differ as to whether or not the decay of rating points is done before or after the weekly RP gain is added to the total RP. I have therefore calculated
both outcomes (the difference being a single multiplicative constant).
It is worth noting that I have assumed the decay rate to be 0.20 (20%). The reason being is that I have seen many other people use this same number, but it may be different in actuality, only more data will confirm.

After plotting the data pairs and curve fitting, these are the best approximations I found.

Using the equations of the lines of best fit, we have:

And so the final Macro looks like:
/script P=(math.floor(GetPVPRankProgress(target)*10000))/100 W=UnitPVPRank("player") N=(W-6)*5000+50*P Q=((W-5)*5000)/0.8-N H=(Q/574.29)^4.016 SendChatMessage("Rank "..(W-4).." "..P.."% RP Total: "..N.." Honor to rank up: "..math.floor(H).."", "emote")
EDIT: Added this macro which tells you how much honor is needed to remain at your current rank progress
/script P=(math.floor(GetPVPRankProgress(target)*10000))/100 W=UnitPVPRank("player") N=(W-6)*5000+50*P H=((N/4)/574.29)^4.016 SendChatMessage("Rank "..(W-4).." "..P.."% RP Total: "..N.." Honor needed to float: "..math.floor(H).."", "emote")
I will update this as I collect more data from my own characters, but if anyone has data from trying the same thing, I would appreciate sharing information to get a better picture.
What I need from players is just their Current RP from whenever they start taking data. Then the New RP values paired with the amount of honor earned in that week (as seen in the first picture).
EDIT: Updated macro and graph to incorporate new data from Henkebenke