That's an interesting agreement. All we have agreed is that 3♠ is a non-serious slam try and 3NT is a serious slam try with 1st or 2nd round control of ♠s (because found our 9+ card major fit on the three level).
If you choose to bid 4♥, will partner know to pass? I know I can't think of any conventional meaning for 4♥ but maybe partner will?
Also, will partner know to bid on with a perfect hand like ♠xxx ♥Axx ♦Kxxx ♣Kxx if North was psyching?