I think this would be a HUGE smash. Eddies take a lot of shards, so even if someone collected 20 shards in an event that would only cover 2/3 of Rainmaker.
They could set a maximum - tiered rewards like before - or even develop some kind of special shard that could only be used in Eddies if they were afraid it would affect farming shards to build other toons (and I don't think it would - too many toons to shard)