It's certainly correct to be suspicious of rewrites, but in this case it _might_ work out okay for a few reasons.
1. The current code hasn't been around particularly long to accumulate subtle bug fixes. So that reduces the amount of hidden know-how that may be accidentally discarded by the rewrite.
2. The current implementation, although it does work, has a number of limitations that aren't inherent in board game implementations, like the poorly-scaling lobby system and the server needing to be restarted every so often because it slows down over time. These may indicate poor architectural choices.
3. The current implementation was poorly-scoped to begin with, like Awaclus mentioned, because it was intended to be a general platform for implementing board games rather than simply trying to be a good implementation of Dominion. By choosing a smaller scope for the new implementation, it should be possible to reduce the complexity significantly.
That all said, I feel like the current implementation is close enough to working that it ought to take less manpower to just patch on a few optimizations and fold some Salvager UI features into the official UI. That would mean that mobile and PC players might not be able to play vs each other, but I don't see that as a big problem necessarily.