Up until the final version (e.g when DMSI is no longer classified as ‘in testing’) the upgrades for DMSI will be free for anyone who has purchased any testing version of it.
After we have achieved the ‘final’ version, then you will have to purchase any upgrades after that. To give you an example, Shannon has decided that all future versions of DMSI until testing is finished and the goals are achieved will be released as part of the Version 3.x branch. Therefore, if you purchased any version from 1.0 through the version before the final, all releases after it for the current major version of DMSI will be free for you.
You will only purchase it once, and get the rest of the versions and the final version of the 3.x branch free.
If there is a Version 4 or later, that will be something you need to purchase again. However, Shannon is aiming to make version 3.x-Final so good that 4.x is unnecessary.