A few things spring to mind here for me, including how to apply this to both single runs and weekly totals
1) if starting from a very low base i.e. half a mile barefoot, for an otherwise fit (in CV terms) runner, 10% may underestimate potential i.e. going from 800m to 900m in a single run or a week rather than say going from 1 x half a mile to 2 x half a mile barefoot may be very easy, but for someone starting from a very low fitness base may be extremely difficult
2) It may be overambitious for those already running long distances, if applied to a long run i.e. going from a 40km run to a 45 km or 50 to 55km is quite a big step in time, even if proportionally small.
3) how to apply this to multi sports where you can't really equate time or mileage i.e. i equate running and indoor rowing pretty much 1:1 in time terms, but I equate cycling to running at pretty much 2.5 or 3:1 i.e. a 2.5-3hr bike ride equates to about an hours run in terms of percieved effort. So if you are doing multi sports with no fixed proportion week to week it's more difficult to do this based on time.
As others have already pointed out, the progression may not be linear anyway, but may be stepped, or even saw toothed for an individual, and one of the most important things is not to take the 10% rule as absolute, but just a guideline and to pick up your bodies own signals.
This is just me as an athlete, I'm not a coach (yet)
1) if starting from a very low base i.e. half a mile barefoot, for an otherwise fit (in CV terms) runner, 10% may underestimate potential i.e. going from 800m to 900m in a single run or a week rather than say going from 1 x half a mile to 2 x half a mile barefoot may be very easy, but for someone starting from a very low fitness base may be extremely difficult
2) It may be overambitious for those already running long distances, if applied to a long run i.e. going from a 40km run to a 45 km or 50 to 55km is quite a big step in time, even if proportionally small.
3) how to apply this to multi sports where you can't really equate time or mileage i.e. i equate running and indoor rowing pretty much 1:1 in time terms, but I equate cycling to running at pretty much 2.5 or 3:1 i.e. a 2.5-3hr bike ride equates to about an hours run in terms of percieved effort. So if you are doing multi sports with no fixed proportion week to week it's more difficult to do this based on time.
As others have already pointed out, the progression may not be linear anyway, but may be stepped, or even saw toothed for an individual, and one of the most important things is not to take the 10% rule as absolute, but just a guideline and to pick up your bodies own signals.
This is just me as an athlete, I'm not a coach (yet)