I think it would be useful to have a tool to be able to log information on a timeline, to start with the tank cycle and continue on with the ongoing maintenance and fish growth, etc. If you could plug in a date and time and attached current water parameters, light timing, water change information, fish size/growth, filter media changing, feeding amounts, decor changes, etc, it would be nice to use this information to build timelines and/or graphs of patterns and trends of the rise or fall of ammonia, nitrite, nitrate, disease, or whatever else is going on in your tank.
If you end up with a problem at some point you could go back to the data and run some sort of report or graph that lets you visualize the information and see, like for example, when you started feeding your fish tubifex worms your nitrates starting rising faster, or certain fish grew more or less according to diet changes. You should have the option to display other data points on this graph that let you check for other trends such as less water changes leading to illness or more water changes leading to healthier growth, etc, etc, etc.
For example, maybe at some point your water starts getting cloudy, so you go back and run a report on your data that may have effected this, such as increased light time, or a new decoration added to the tank, or feeding a new type of food.
If you even went as far as to log information for specific fish in your tank, you could go even further with analyzing your data. The more data you provide to the program, the more data points, more accuracy, and more trend comparision and cross referencing could be done.
The next step, is based on the results of your data, the program recommends possible solutions to any problem you may be having based on your individual and personal data, not just what is typical of the average aquarium keeper.
I hope you have a lot of free time!