Honestly, ending after ten years might be for the best.
The two-season renewal means that Steve Levitan and Christopher Lloyd will be able to plan the plots out well ahead of time and make sure that they hit all they beats they want to before the end.
A series finale at the conclusion of Season 10 could be exactly what the show needs to end on a high note with all fans, unlike a certain other long-running sitcom that came to an end in recent years.
The show has more or less kept its story momentum going, but it might become hard to believe after a while that all these kids have found reasons to hang out with their parents and adult relatives on a regular basis.