I think this is a fantastic initiative!
By drastically lowering the risk and financial concerns for existing sellers, this scheme makes them more likely to stay with the platform and invest further, and it also makes the marketplace more attractive for larger players to adopt - ultimately this means more sales for Brandroot.
I would like to see this scheme simplified, whereby the entire sellers share goes towards settling the Brandbank loan if necessary (I hate owing money) and the account handling fee done away with. This alternative will make for a more financially robust platform, require less admin, reduce potential for accounting errors and is easier to explain to sellers. For me, by far the most important advantages of Brandbank are the peace of mind that it would offer during slow sales months and ensuring that I won't make a loss due to renewal fees. I am not concerned about making a profit from every sale - only the net profit at the end of the year. If you want to make up those handling fees elsewhere, I think it would be better to do it by raising listing fees slightly.
I would also modify the following rule with a clause: "Sellers taking part in Brandbank cannot remove their domains from Brandroot while their Brandbank is active, unless replacing them with domains of equivalent or higher value."
The main reason I say this is that I would like to be in a position to replace the worst names in my portfolio with better ones on an ongoing basis, which will increase my likelihood of sales at a decreased cost (by reducing renewal fees in the long term), and increase the quality of the marketplace, which will attract more buyers. Names with a low probability of sale will end up costing a lot more than their initial listing in renewal fees, and it is better to get them out of the system.
Another thing I like about this scheme is emphasizes the importance of accepting high quality names, since Brandroot is taking on unnecessary financial risk by accepting a dud. Increased quality is good for everyone.