No cons that I can think of. P. 'Shenandoah' is a great grower, maturing quickly and it is a real beauty. I only grow Schizachyrium 'Prairie Blues' but I would grow many more named varieties - they are lovely. There are 2 Eryngium with the common name of rattle-snake master E. aquaticum and E. yuccifolium, I assume you plan on growing E. y., not that it would matter because I like all Eryngium. I think it sounds like a wonderful combo of plants. Where are you located, just the nearest big city?

Here in OKC there is a large grass planting I like to drive by just to look at it. It has large swath of Little Bluestem massed in and behind that is taller Switchgrass which is also massed in. The Switchgrass looks like the species rather than a named type. In front of the bluestem they planted lower growing blue grama. The effect is quite nice as the massed plants get taller from front to back and it shows up the variation of height and color due to the mass planting and each type being separated rather than mixed together. They placed some large rocks in front with some Hepseraloe planted here and there which makes a nice contrast that echoes the grass in shape but with thick leaves and pink flowers on tall stems, its the only color and the simplicity is very effective. Behind the grasses are cedars which looks especially nice in winter with the light winter color of the grasses contrasted against the green. There are also bronze statues of realistic buffaloes, a mother and two babies which is a nice effect. If I had the space I would try to copy it. A crew cuts it back each spring but other than that its self maintaining.

Another native native grass that works well is SideOats Grama which is mid height. It forms seeds early, each mature plant forms a thick tussock that has hundreds of stems with seeds that catch the light in late afternoon. They reach maturity in a couple seasons.

Thank you for the input. We are near Kansas City. On the MO side of the line. E. yuccifolium was my thought. I'm going to move ahead, when I can, with the switchgrass/little blue combo. At this point it may be spring before I plant. Not optimal I know but I work in things as I can. I'm still trying to get trees in before the freeze. I would like to work some limestone rocks into the backyard "stylized prairie". That's one reason the grass will be planted in spring. I've rock available now, but I've got to move and place it.

I have a base of bluestem , seep muhly , love grass, black gramma and invasive KR bluestem that stays fairly short on my shallow soil. I am then trying to plant drifts of taller grasses in the sea. It is a dry area so I am going for Muhlenberia emersleyi which looks like the indigenous big muhly but is from west Texas to Arizona. It grows well in this difficult area.