Having NO restrictions is a terrible idea. Every single pvp battle would become a stalemate, with each player constantly playing defensively with their Aces. I guess you might get some mileage out of Plus and Same rules, but for the most part the game would become incredibly stale.

Having new restrictions with one or more 4* cards allowed - that I can get behind. Right now 4* cards are completely pointless outside of Random rule - and even there, when you get a 4* it's all "Eh, not bad, but kinda wish that had been a 5* instead." Allowing decks with composition 33345 would be cool.