I am of the opinion that there are different types of tanks that are set up to cater to a specific livestock type. LPS/Softie tank, Anenome tank, and SPS tank have differences that in the long run allow the livestock to thrive.
On Average, an SPS tank would have more intense/stronger lighting, higher flow, and a lower nutrient level than an LPS/Softie tank, and the params with SPS are far stricter than LPS/Softie.
Conversly, a lagoonal type tank would have lower flow, deeper depth simulated lighting, and a higher nutrient level for the LPS/Softie to thrive.
As an example, before I went all SPS, my LPS and the few shrooms/rics I had never grew and were contantly beaten by the current. I placed them in a nano with less light/flow and "dirtier" water and the took off. As an example of the reverse, a digi hitchhiker that was on a piece of LR only lasted a few weeks before RTNing.
Though these are the "ideal" models I have observed that create the best results for the two types, does not mean one can't keep a mixed reef, but you may have to make concessons on exactly what you choose to keep. Mixed reefs are the ultimate balancing act, and the aquarist needs to be a "jack of all specie". In the aquarium world to have one with mixed rare and exotics is what I was eluding to with concessions one would have to make. How would you feel if you bought a frag of "tuiti fruiti" flavor of the month SPS for $100 a 1/2", and an $8 dollar Condy anenome took up residence on it? Because I value SPS more, the Condy would be gone........and gradually skewing my tank to an SPS only.
SPS can be added to a mixed reef very well, but it may decrease your abiltiy to get it to color up and grow at an optimum rate of the more finicky types that may not grow in less that perfect conditions.
Can it be done? Yes, but I don't think you will be able to choose ANY type of SPS to put in. I would imagine you would have success with Caps, digis, and all the other "starter" SPS that tend to be more fogiving and try to avoid the more exotic flavors that do better/require a SPS specific tank for the best results.........but I will bet that eventually you will love SPS and only go with them to be able to keep the exotic SPS like I did, or decide they are too much trouble and stick with the others.