In Workload view, add an option (e.g. "Remaining Weekly Capacity") so a person's weekly capacity drops automatically as each working day passes, based on the Workspace work schedule. For example, with a 37.5h week (7.5h/day, Mon to Fri), capacity would show 37.5h on Monday, 30h on Tuesday, 22.5h on Wednesday, 15h on Thursday and 7.5h on Friday. That's 20% less each day.

At the moment Weekly Capacity is fixed for the whole week, so by Thursday someone can look like they have room for 20+ hours when really they've only got two days left. If capacity counted down, managers could see real availability for the rest of the week and stop overloading people late in the week. Daily Availability can be used as a workaround, but you lose the weekly overview.