I think there might be a mix-up in how DTI is defined by institutions like the IMF and how it is used by, e.g. banks.
I got this from this link
debt-service-to-income ratio (DSTI):
The maximum DSTI ratio for housing and consumer loans is set at 40%,
where debt-service (DS) is the total monthly aggregate of credit payments to financial institutions and ...
Has any other state done anything like this before? Who, when, where?
Yes, one (relatively) recent example from 2010 is EU member states guaranteeing portion of Greek debt see the Guardian article about it (although technically the countries are all in loose (con)federation).
Another example could be UK guaranteeing Irish land bonds in between 1920–1938 (...