Caution: speculation notice. This article deals with things and events which may be revealed in a book as yet unpublished. While based on firm data from previous books, its assumptions may be denied at the whim of the author.
The potential is there, in a city full of innovative talent, to really make this a city to be proud of. Recent rediscoveries of long-forgotten but still serviceable relics like the Cloaca Maxima suggest that for the first time in many thousands of years, the city may end up with a sewerage system that works. Combine the extant drainage system, represented by the Cloaca, with Sir Charles Lavatory's patent system and Harry King's ability to make brass out of muck, and you have a modern network of sewers which obviates the need to chuck it (i) out of the window, or (ii) into the Ankh, or (iii) both, and at the very least there will be cleaner streets to walk on. As well as a very profitable recycling system situated far downwind of the city.
Recently, visiting Dwarfs excavated an impressive and far-reaching network of tunnels under the city, following an agenda of their own. Although these Dwarfs are now long-gone (apart from those facing the justice of Vetinari and the Low King), their tunnels remain, no doubt tended by native Ankhian Dwarfs who in their very dwarvish natures would be reluctant to allow Dwarf-made underground works to go to ruin. (Perhaps maintaining these tunnels allows Ankh-Morpork's Dwarf population a harmless, productive and above all, free-to-the-city way of safely connecting to their inner Dwarf). Any Dwarfs performing this work would no doubt be aided by the impressive array of drainage and pumping devices that the builders left behind when they departed in something of a hurry, the most notable of which would be the Technomantic Devices seized by Vetinari under the legal principle of Eminent Domain, or Quia Sic Ego Dico (Because I Say So), supported by a secondary argument of Acquiris Quodcumquae Rapis (You Get What You Grab). No doubt Mr Slant has laid out the City's legal case in a finely-argued and impeccably presented case to the Low King, bound up in the usual thoughtful legally binding red tape.
The Dwarfs are no doubt aided by the Artificers' Guild, to whose care Vetinari has turned over the Devices. Forward thinkers have noted that the Dwarfs laid rails in these tunnels, so as to most efficiently manipulate and remove wagons full of spoil to disposal points. What if, the thought goes, similar wagons might be built on the same principle to transport humans between points of interest in the city - but Underground, below the congested streets....
To do all this requires money. Vetinari has set the ball rolling by reforming the Royal Bank of Ankh-Morpork and the Royal Mint and is now virtually guaranteed a loan of half a million dollars. Other forward-thinking citizens such as Harry King have also been investing heavily in areas of their own professional expertise.
But loans need to be repaid, which is why Vetinari has plans to reform the taxation system, as only through raising taxes can a Government fulfil its fiscal obligations and prime the pump for future prosperity.
It is all about the city, as Vetinari remarks to Moist von Lipwig - nothing is too great a sacrifice or risk when the city and the future Vetinari foresees for it is involved, even going to the lengths of employing known criminals in the hopes that they will succeed, and if they die trying it's no skin off the city's collective nose as said criminal was sentenced to death anyway.
Moist takes this adage to great lengths, emblazoning the legend AD URBEM PERTINET on the new paper money. This has to have given even Vetinari a moment of pleasure.