The Plus license was really guaranteed updates within version 1.x – this follows the traditional desktop software sales model where each major version is a different purchase/paid upgrade (i.e. MS Office 2010 and MS Office 2016). But it’s not a forced upgrade as no one will lose access to Insync (1.x) 
As for the distinction, we wanted to gift customers with a free upgrade (for the confusion these past few days regarding the new pricing) but we simply can’t provide everyone with a free upgrade (as our CEO said, we might not be around much longer if we do so 
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