What is this amazing functionality it supplies that I can't already get?
Well, not sure how you do things however I like to spend the least amount of energy be it time or money in development.
The fact that it would be officially supported is the amazing functionality you speak of......
Nice to see updates for Blitzmax, not so nice to see updates that break 3rd party plugins and require A. Waiting for the 3rd party (if they are still active) to update to accommodate and B. enormous rewrites on your behalf due to the changes breaking how you do things with said 3rd party software currently.
A supported solution would mean that any changes to the core of Blitzmax would be tested in it's officially supported plugins (and updated accordingly) prior to release. Max3d, being from BRL, would naturally be tested with the updates to Blitzmax (or at least considered during the update process) to ensure that the changes are less intrusive.
I'd be more than happy to see Leadwerks engine become an official plugin if one were to have to choose an alternative to Max3d however until that day comes I cannot invest countless hours on a 3rd party tool just to see Blitzmax get binned or some update break the entire Leadwerks wrapper...
Time is money, and something unsupported is nothing but that.... Unsupported.... Just because someone CAN write a plugin doesn't mean it will always work through the thick and thin of the Blitzmax update process (or lack thereof).