Pretty simple. At the end of the season, your assistant manager simply files a report telling you who has impressed in the reserves/youth sides, what loaned out players managed to achieve and feedback on players who he doesn't feel will make the grade and should be released. This could simply be entered into the inbox for pre-season, as I imagine something fairly similar to this probably happens for most clubs at this time.
Anything extra at the end of the season would be good for me. At the moment things just sort of tail off after your last game until you get to the transfer window or your start of season expectations where you can set yuor transfer budget.
I think making managers more aware of how their players have performed is only ever a good thing and we could build up a good picture of how our teams progress with a bit more feedback from our coaches and scouts. Maybe something as simple as summarising the current coach reports you can access at any time would work. So at the end of the season your AssMan would tell you which players you should think about selling, which youth or reserve players look like they could make the step up and so on.