So here is an idea that should make existing customers happy, while applying your new sales format to new customers. Like many others, one main reason I chose Maxwell Render was for the bundled plugins. At times I have used Lightwave (unfortunately this plugin is going away now) and liked using Maxwell within the Lightwave software. I have now moved on to Blender, but there is no official Blender plugin as yet (though it looks like Maxwell version 4 will have a way to import Blender scenes (.blend files) directly!). So now I will be using Studio. In any case, I think many of your existing version 3 customers use Maxwell because of the large number of included plugins.
Why not offer, say, three or four plugins INCLUDED with the upgrade from version 3 to version 4 for your existing customers? This way, existing customers are kept happy and the software maintains the selling point many of us purchased it for. If an existing customer, in the future, switches to a new 3D modeling software, then they can purchase the new plugin at that time (I doubt most of us use more than 4 model programs). As for NEW customers (those who will be purchasing version 4 without having owned version 3 or prior)- your new sales tactic can go into effect now, ie: brand new customers realize that Maxwell plug-ins are sold separately. They, as new customers, will either accept this or not, but if they accept it their expectations are met.
Existing customers are happy because the promise of multiple plugins is kept; new customers are happy because they were never promised free plugins; and NextLimit is happy because they have met customer expectations (and will have future revenue from the sale of plugs to all new customers).