I think the maximum overstones are going to be pretty great, actually, even with the high requirements, just because waystones in general aren't a thing with a ten year shelf life, riverine transport is very comfy, and what elves and dwarves lack in speed they make up for in not dying of old age in twenty years after getting good enough to contribute. The logistics are there to get this product out eventually, and the important polities involved -- the important specific individuals who will be doing the work -- have survived for millennia. It'll be harder to forget this time.
I have sensed on the horizon a more interesting possible stretch; a purely mundane waystone.
[?] [CAPSTONE] [Sky Metal]
The original material from the golden age, but strictly speaking a purely mundane alloy that's merely very precious. The advancement of material science might eventually allow for the production of these without the help of magical forces.
[ ] [RUNE] Carved
Requires a mason. Trivial, negligible cost.
[ ] [STORAGE] [Cheap/Moderate/Expensive] Material
No requirements. Trivial, low/moderate/high cost.
[ ] [FOUNDATION] Clockwork
Required an engineer or clockmaker. Moderately difficult, low cost.
[?] [TRANSMISSION] Leyline
Requires a speaker of Anoqeyån or Lingua Praestantia. Simple, trivial cost.
[?] [TRANSMISSION] Riverine (Spirit)
Requires negotiation with the river's spirit. Reduces difficulty and cost of Foundation. ? difficulty, ? cost. Reduces difficulty and cost of Foundation
I thought there would be more remaining, but after eliminating the options that require the creator to be entirely a wizard I think we're just left with a goal (of finding out how to manufacture titan metal) and a question (of if you need to be magical in order to speak the magical languages involved with setting up leylines, or else magical in order to communicate with the spirits of the rivers).
You know how we didn't need to worry about the logistics of the canal because it was a manpower thing and that meant that the Tzar could just do it on a scale we had no way of influencing?
Imagine that, but every stoneworker in the Empire setting up rocks as a hobby -- or a form of prayer.