In general, I too would completely welcome regular flash sales. I want another impulse buy like Persona 3 FES some months back (it was 9.99 I think, I scrambled to get home and purchase it based on word of mouth review). Heck, promo some solid lesser known games too, I know PSN has got to have a ton of gems on it, I just don't know where to start.
Problem is, until Sony makes a proper clear statement, I'm really hesitant to trust any kind of digital promotion at the moment. If I have the option to choose physical, I'm not going to spend money on a PS3 digital game only to be told that I can't play said game on the PS4. If I wanted to rent the game, I'd go to Gamefly or someone *mumble mumble*. I guess if this was something that started regularly on the PS4 and not the PS3, I'd still welcome it.