Yes, all the maths you need to scale, mix, etc can be done in the UVs, up-front and sharable with any of the layers in your landscape. Stochastic-sampling does this quite well IMHO.
To my experience you can do (almost) all your UV manipulation up front and recycle those results across the remainder of your material.
Yes, adding in a detail-normal, distance-blend, etc will invoke another sampler. My suggestion was if you do use one there is a path to get double-duty at least, you could use it for up-close as well as far away, assuming you have a middle-area where neither is applied, else you will have a line when you flip the UVs.
Texture-bombing and other related techniques do require additional samplers, which is why I leapt on Alex’s method Since the triplanar is 1 sample you can then UV-futz to untile and it should still be a single-sample (which it is).
EDIT: I will point out that what works for organic-textures like grass, rock, dirt; one’s that don’t have a lot of regularity doesn’t work for things that tend to tile, like Tharle’s example above. There’s awesome ‘randomize my tiled-floor’ techniques and you can do things like add imperfections here and there to spice things up, but that regularity works against the stone/rock type materials, so you will likely want to learn a mix of techniques depending on what you want in the end.