The post says that, at least for the time being, nothing is going to change for their users. Hopefully you wont be forced to sign into Pinterest to use Instapaper.
Except a new third party (Pinterest) will sooner or later have access to my Instapaper data. I trusted Instapaper because they had a sustainable business model not based around ads. I do not trust Pinterest because their business model is based around selling my personal information and activity to advertisers.
Basically it's time to stop using Instapaper :(