Format can cycle unless people specifically want 1 format. We're playin on cockatrice so I mean we can use whatever. Maybe the format would be standard for week 1, modern week 2, maybe cube? Idk people can comment since I don't want to exclude anyone's opinion.
Cockatrice is all about using cards before you buy them. If we are only allowed to use cards we have, then some players will have an unfair advantage or disadvantage. If we can use any cards, everyone is on an even playing field. This applies to all formats.
I think the only rule we should have is no p9. Even if we are only allowed what is restricted, there is no reason that someone would NOT run 1 copy of ancestral recal and 1 copy of time walk and 1 lotus. Since this would be the case, eliminating the p9 would make it more about deck building skills and less about who draws their singleton restricted p9 card.