I mean, that's *an* option, yes. But making a cheaper leyline only waystone would save some money. And probably quite a bit of labor hauling multiple giant blocks of stone around different places. Though I suppose the swap out option would build some reinforcement into the network by adding the river redundancy in places.
The other advantage is that this would allow us to reshuffle chains of Old Waystones from areas where they're less needed to areas where they're more needed. There may be, say, a line of Waystones that goes across country through uninhabited (by humans) forests before intersecting with a settlement on a river. If we can place a New Waystone in that settlement we could possibly remove several Old Waystones down the leyline from there, which could then be moved to where they're more useful.
There are also those Waystones we know of in Sylvania that are part of orphaned segments of the network that are channeling Dhar down leylines until they hit a missing Waystone.
We could then use these to do something like erect a temporary line of Waystones as a bridge to the main network from the end of a line connected to another nexus, and then reorganise the existing Sylvanian Old Waystones to feed into several New Waystones on the river. Once that's done we could disconnect the temporary link to another network and move the Old Waystones used to make it somewhere else.
This would hopefully only take a few New Waystones but would get a much larger number of Old Waystones that currently aren't connected to the wider network working safely again, not just making one place a bit cleaner and another much more corrupt.
Similar things would hopefully be possible with regards to the Black Water. We could build a temporary link to the main network with redeployed Old Waystones, then line the shores of the Black Water with permanently redeployed Old Waystones from somewhere in less urgent need and a single New Waystone at the headwaters of the Skull River. Then, after the leylines linking them have been built we can disconnect the temporary line of Old Waystones are redeploy them.
The main point is that we shouldn't look at places where we can swap one New Waystone for an Old one, but where we can swap one New for multiple Old, and what we can then do with small numbers of New and larger number of Old Waystones.
After all, that's the situation the Old World is likely to be in for a long time, so we should look to how we can optimise that mixture, including by passing through configurations that aren't permanent, but just exist temporarily to directly connect to the wider Network so leylines can be created, and then disconnected leaving isolated segments of the network linked to the wider while only by rivers.
