That's actually something zanz is/was considering: create more nymph-like cards so that eventually people can create their own unique deck. Downsides? (Perfectionist) Collectors will suffer (a lot), and people who dislike "luck" will rage.
This is true, though if the nymph-like cards were obtainable by skill, rather than luck, then it would be one way to separate players more based on skill level, which this game needs. (and being a perfectionist and a collector, if they were luck based I'd go insane... it already drives me bonkers needing to farm hundreds of nymphs/marks from the oracle and tourneys :p)
That won't cut it. Assuming the cards were obtained by reasonable amounts of skill (i.e. not so ridiculously difficult that luck plays a huge part), then eventually (a long time is needed, but it will happen) there will be enough people who again manages to collect effectively all cards, makes the best decks, and everyone plays the same decks over and over.
If you say that "a long time" is so long that few people manage to get those cards within some time period, then everyone below the "threshold skill level" continues to have this same problem of playing against the same decks. Nothing has changed for them. They'll occasionally get to play some unique deck from a "skilled" player, but that's equivalent to them getting lucky and playing an original deck right now. In addition, skilled players will have new toys, but they'll still be facing the same stuff. So nothing really is solved.
So I way I see it, if the problem is to be fixed, you've got the trade-off I mentioned. Otherwise, periodic new cards, nerfs, etc. are the best bets to temporarily upset the equilibrium and keep things interesting.
