@Tim: it looks like you have OSPi, which unfortunately does not have current sensing circuit. Only the fully assembled, microcontroller-based OpenSprinkler 2.3 (AC or DC) has current sensing circuit.
The sequential group is actually the opposite of what you have in mind. Stations in the same group are serialized, whereas stations in different groups can run in parallel. This is common in situations where you have many stations, and they run on different water lines. So stations on the same water line will be serialized to reduce impact on pressure, whereas stations on different water lines can run in parallel. What you have in mind is that stations in the same group will run together / in parallel, and stations in different groups? I am not sure, perhaps you want them to be serialized? As I said, if we are to accommodate both requests, then there needs to be a way to generalize the two types of grouping. The challenge is to make sure the scheduling algorithm does the right thing when you start using the grouping feature arbitrarily.
@NOV6: I think the main benefit of a calendar-based program is the ability to schedule the same station multiple times in a program. I am curious how often this is needed. Note that the current OpenSprinkler firmware already allows the same program to be repeated multiple times, but of course this means all the stations will be repeated (as opposed to some repeated and some not). Anyways, just want to get a sense of the common use scenario.