That said, the Supreme Court also had language suggesting that one reason it decided in favor of South Dakota was that its requirements weren't onerous. This might suggest, for example, that states should have some minimum threshold but the decision didn't supply one or state so explicitly.
IANAL but, if I head to guess, this isn't going t be an apocalypse but there are going to be some uncertain times, some state will probably push the boundaries, compliance costs will rise, many small businesses won't comply and try to fly under the radar especially given it's not clear what teeth a state has against out-of-state retailers with no physical presence, etc.
Bonanza.com probably stands to gain the most from this. Shopify and similar products will likely adapt to gain as well. WooCommerce and other “self-hosted” shops might actually end up dying from it.
Unless I'm miss-understating, this ruling makes every company that sells online subject to the local tax law in every state they make a sale in (for even small companies this can easily be most of the 48 continental US states). The concern is that every state will have different rules for exemptions and filling requirements, so even knowing if you are exempt and/or need to file is going to be a significant cost for a small businesses just to be sure they are in compliance... even if they owe no actual sales tax.