Maybe I don't understand what you're saying. What kind of observations does evolution predict that we're not seeing?
To be honest, I think that evolution would only meet the conditions you describe if the environment were constant. Since it is most decidedly not, due to the interdependence of species, and also due to global environmental changes (e.g. ice ages), I don't think evolution could be described as a steady-state process. I may be wrong, and this is not a scientific opinion, but I would need more convincing to see evolution as a steady-state phenomenon.
Even then, though, the calculation you describe would be interesting, because we could assume that evolution would probably work at about the same rate on average in any environment, since environmental changes are most likely very slow anyhow. You're assuming that the rate will come out to be something observable, of course. What if it comes out to one every 300 years? We haven't been observing species all that closely for 300 years yet. And then, do you include bacteria that become resistant to various medicines? Could that be considered a new species and the old an extinct one?
I'm not supposing answers to these questions. I don't know them. If the rate of speciation comes out to one every 10 years and we're not seeing it, then evolutionary theory is going to have to change or be replaced or whatever needs to be done, but I can't say I've seen any such calculations, so I'll withhold judgement until I do.
Let me try again. Time cancels out of the equations in a steady state process. The RATE has nothing to do with anything other than determining the PERCENTAGE of the biosphere that will be undergoing speciation at any given INSTANT in time.
Considering there are something like 100 million species on the planet right now, the speciation rate would have to be infitesimal not to see ANY at any given moment. It would have to be so small in fact, that it would violate the rate evolutionists claim is demonstrated in the fossil record.
In other words, speciation rates, calculated from the fossil record, should allow us to see substantial speciation in the biosphere, especially among organisms with high reproduction rates and short lifespans.
And ring species don't count, since they are an historical construct. The theory predicts we should be seeing speciation WITHIN a percentage of the biosphere AT THIS INSTANT in time, not over a geographic area, not over a time period of a thousand years, but RIGHT NOW.
And changing environmental conditions don't count either. Environmental conditions determine which speciations SURVIVE, NOT which speciations OCCUR.