1. If there is provision for changing path of sub test
Case: when user copies subtest manually to a folder and inside subtests will not be available in order use the test, if a testbox provided like Content match provided it looks good when we custmize scripts. 

2. Allow sub test script add without search
Case: when it has 1000 scripts in a project, then it has to load all the scripts and search
it will take 2-5 mins, instead have + to add script if above Case is implemented.
Any way while running your validating whether script is available or not.
I think this will make a value add.

Hope that above will make User friendly more :)

Thanks,
Gopal K