I'm moving my votes here instead:

https://gnucash.uservoice.com/forums/101223-feature-request/suggestions/14368269--fund-accounting

The existing budget tool cannot do zero-sum budgeting at all -- there is no way to ensure that you are not budgeting more than you make and/or have (other than constantly manually summing the values).

Currently, I am using the work-around suggested by Bob Brush. Basically, I have to consider only two categories of accounts: those which consider debits positive, and those which consider credits positive. Asset, Bank, Cash, A/R, etc. are debit; Liability, Credit Card, and A/P are credit. Fortunately, all of those accounts can be mixed as subaccounts. Income, Expense, and Equity (and others) are very restrictive on their subaccount types, though.

So, I record my "assets" in a debit account and it turns out that almost everything else uses a credit account type. For example, I am using the Liability type for both "income" and "expense" subaccounts. This orients the totals correctly (black/red) but makes the labels confusing, so I have had to switch to using the formal accounting labels. As far as I can tell, all of the debit types are equivalent and all of the credit types are equivalent other than their labels in the register. Using formal labels makes them exactly equivalent. So, now, I am only using the Asset and Liability account types.

I tried using Income and Expense accounts since they can be mixed, but they are both credit types, so "assets" all end up with red balances. I don't understand why the account types can't be mixed. Maybe some reports care about the account type? If so, this workaround cripples reporting.

You also might want to look at the budget feature and use that, it allows full use of all the accounts, so you can do the kind of things people do, like rob savings accounts, credit cards.. but still keep the over all goal in mind. On the sample file you linked to try this: On the menu select >>Action>Budget>New Budget, now select >>Edit>Budget Options.. Change the date to a relevant date, in this case 2013, and I would rename to something specific, you can have His Budget and then later Her Budget, or What I Want vs What I Need.. Now expand all the sub accounts by clicking the plus sign next to them after that press "Ctl+a" on the keyboard to select all accounts, and then on the menu >>Edit>Estimate Budget.. It will autofill in based on the existing data.. Now you can change any of the cells to what is needed and even change the date to this year, ect.. Cool?

I might not be understanding what you are trying to say, but I think that you can accomplish this goal using the existing account types. If I was going to try this, maybe make the top level account an asset or accounts receivable type, and then make sub account (the plan) of type accounts receivable, and the other sub account (expense plans/trackers) of type accounts payable. These types will automatically zero out as you enter things in both registers. Note that you can change the type to A/R or A/P and the color in the list of accounts will change to red or black, but the math gnucash does underneath doesn't change. So if you enter data in the reverse order in one or the other accounts it will sum both sub accounts regardless of their type.. this can be somewhat confusing, but don't worry gnucash is coded to sanity, so most of the things you can't do will be things you really can't do, like spend the same money twice, ect..
It may take a few trys to help model the exact situation.

http://www.gnucash.org/docs/v2.4/C/gnucash-help/acct-types.html