As I view it, payment or non-payment of debt is not directly scored. FICO is a risk analysis of liklihood of future delinquencies.
It is true that the level of current debt can contribute to the increased liklihood of future delinquencies. Prediction of liklhood of future default based on events that have not yet occured is indirectly included by looking at items such as your current % util of your existing credit, so FICO does make guesses. It combines those predictions with actual historical delinquencies, which dont involve guesses or predictions. They are fact. So past actual payment history combined with current utilization of credit account basically for a whopping 65% of FICO's crystal ball.
The payment or non-payment status of debt is not scored directly, but rather indirectly through delinquencies that are reported when debt is not timely paid, and by the percent that debt claims of your existing credit limits. On the flip side, paying delinquent debt does not in and of itself improve one's FICO score.
So I look at it from the perspective, disregarding the issue of account closures, that entering into a plan to pay only interest will reduce the chance of actual delinquencies occuring in the future, and thus forstall future hits on your FICO score. But paying only interest wont reduce the principal balance on any account, and thus wont result in any improvement in % utilization. So FICO stagnation.
While this may be a bit oversimplified, in my opinion (disregarding the speculative issue of possible account closures), such a renegotiation plan would appear to be basically FICO-neutral.
