Your standards are too high.
Personally I'd be happy enough with a code that reliably computed equilibria for species & reactions I chose.
For each possible species, you would have to type the formation enthalpy, entropy or Gibbs, heat capacity (possibly a polynom of the temperature). Then, such a software is but more than a spreadsheet. I bet it exists for Mathcad/Maple/Mathematica/Matlab/etc.
Wouldn't you expect the software to equilibrate all the reactions? This would avoid mistakes and save time. Between just two reactants and three products, there are already many reactions and error sources.
You'd get tired very soon (or at least I would) to type thermo data again and again at every use, every equilibrium. The very minimum I expect from such a software is that is knows the thermo data for all usual small molecules like H2
0, CO, CO2
... there must be 100 to 1000 of them.
As well, the software better knows the phase changes for common compounds, in order to avoid elementary mistakes.
And so on and so forth... My bet is that, as soon as someone has a little software that works in one particular case (say, only aqueous ions) he will immediately want to make it more general.
The best strategy looks like:
(1) Find a software that already exists, or
(2) Let a university develop it for free, then put your company's name on it and sell;
(3) Make the soft very general from the beginning, but start small. It looks like a many-years project.