I think a really useful feature of the calendar would be the ability to schedule optional workouts and have these clearly distinguishable from other workouts at a glance. For example, I am about to start SSB LV II. I’m doing LV as I know that I can commit that much time, but when time allows I do a couple of extra workouts each week. It would be nice to be able to add these to my calendar as optional (maybe shaded in a different colour) so that at the beginning of the week I can see at a glance which 3 of the 5 workouts are part of the LV plan, and which ones I have added as extras. This would make forward planning much easier and any reshuffling of workouts during the week (which I find is ofter required) would be quicker. I appreciate that this can sort of be achieved by using annotations, but this seems like a long-winded workaround.
Even better (for me) would be to enable the selection of specific days as optional in a training plan. For example the difference between MV and LV versions of SSB II is one sweet spot workout and one endurance workout each week. If it were possible to select these two workouts as optional when populating the calendar with a training plan then it would make my life a lot easier.
Finally, if planned optional workout TSS could be distinguished from other planned TSS in the chart at the top of the calendar then that would be fantastic.