There have always been cashless decks, it is just more explicit with the debt that you can do this.
For instance, take something like Wizards, Remodel, limited draw (e.g. Lib, Wt, Ronin), and some villages. If the kingdom has no action/$ cards, then tossing in silvers, golds, and or other treasures can be problematic. You can gain $4s, trash a recoverable $6 to a Province, and draw your way through. The reason this stuff is rare is that you need to combo a lot of stuff get both enough draw and value gain while also not wanting cash.
Debt makes this easier because once you commit to cashless, everything gets way more powerful.
You don't need strong trashing to make this work, beyond hacks like Banish, you can get buy whenever you can boot strap enough draw to do what you want. Imperial envoy for instance is quick build out to mountains of debt without trashing if you can just gain them from Craftsman. Artist is finicky, but you can some huge amounts of draw with the right setup (e.g. double Haven/double Artist with Bm). And of course there were older ways to quickly bootstrap up.
The big players here are Craftsman, which is roughly a terminal Gold if you want to spam $5s, and Gold Mine (which is arguably a magic gain $6). For the rest, if you figure that you will be pairing some of their draw with golds to get back to $0 debt, the jumps in power from ignoring debt are a lot less dramatic. Ie needs a silver to become a Hunting party with a +buy (or a gold for every two Ie's). The former suggests that it is an ~$8 Hparty with +buy and the latter is a half card better for the same price. Litter needs a gold for everything 3, so we are talking about a slightly less cost effective Lost city. Panic, Harsh winter and a few other odds and ends look like they will make debt loading more feasible.
But debt maxing is not remotely unheard of. On a Horns of plenty boards, the optimal play on a lot of Mountain pass boards is to bid $40 as soon as the other guy gains a province. If he nabs 5 provinces, you can beat hit with 3 Provs, 2 Duchies, and the VP. If he fiddles around, you can bury him (assuming you are both going off the same turn) for 5 provinces and 8 VP (getting up 20 VP via the duchies requires getting at least a 7:1 split). Obviously there are caveats, but the Craftsman and to a lesser extent Gold mine just make it more common to load up on debt and to then forget it.
