What costs Infuse 5 for Infuse 4 users?

I have bought Infuse 4 for ATV 4 fro 9.99 EUR just in February 2016 and thought it was a lifetime buying. Now Infuse 5 came out and they ask for 12.99 EUR it. This is very very sad. If I knew this before I would use Kodi with Sideloading whicht will gave me much more functionality.

The annual subscription of Infuse Pro is currently on sale for 30% off through the end of the year.

More details on this can be found here. Infuse 5.1 - Search & collections | Firecore

Should I have to pay again if V6 is released?

The Infuse Pro subscription will cover all updates, even major ones like v6, v7, etc…