Why would votes being public make it so that alt accounts (throwaways) would be less effective than they were on reddit or any other public forum?

I think privacy is important but even in public online places, like the fediverse, it is possible to maintain anonymity if it's desired through curation of what information you post, where you post it, and with which account.

Will the test instances be publicly available?

That would be greatly appreciated by us over at /m/kbinStyles so that it’s possible to see that everything still works before the new version goes live.