I'm in favor of gold nuggets (or coins, texture-pack dependant) being the base currency unit. We can also still call it the septim, much as we do our current 'virtual' septim. Since there's 9 nuggets in an ingot and 81 nuggets in a block, it allows for easier trade of smaller quantities of items (like lapis or bookshelves or clay). It makes it easier to fix relative values for materials, if we so choose (though I wouldn't). Really, it wouldn't change much from our current system, except for a slight adjustment in how we value things like a block of land.
ie: current system: 10 septims/square of land, 50 septims/ingot = 5.56 septims/nugget
new system: 2 nuggets/square (equivalent to 11.12 septims for our current economy)
So... Things might get slightly more expensive when working based on septims, because we're working with a base 9 system. Though this isn't necessarily a bad thing - more valuable land should be the case if we're planning on having the next map longer, since it is 1.0 and all.
(Now if only they'd stop pushing new updates on us so freaking soon. Take a chapter from the book of Terrarria, Mojang!)