The ability to go back and edit a custom made route rather than going to test it realising it dosnt work then having to start all over again. You can edit things like car types,weather etc but not the route itself
So if your track dosnt work you have to start all over again
You say the same as I did a while back:
https://forums.forza.net/turn10_postsm1205306_Wishes-from-a-Route-Creator.aspx#post_1205306
+1 on the ability to edit your own saved routes is something that the blueprint builder is seriously missing.
I think Mario Maker is something that can provide some great inspiration for what the FH5 blueprint builder should aim for.