As part of a larger data project I'm reviewing the various unit files and it brought me to two unsupported unit folders - Unofficial and Unsupported.
The unofficial folder:Is made up of units from various out of print fan magazines, Mechforce, video games and fan sources. This folder has approximately 1500 units (1200 mechs, 300 non-mechs).

The
unsupported folder are units that basically MegaMek only partially supports. For example old model LAMs not made to the current construction rules these are currently the only units left.

We really have two options for these folders(units).
Option 1) Move the folders to an unofficial download that players can choose to add to there games. This option means out of the box the only units you see are canon; and will reduce the number of units by around 1500. I should add lots of these units have been remade and rolled into canon units by CGL over the years.
Adding would be as simple as - download the files and put in your data-mechfiles folder, delete units.cache, start Megamek and they are back.
Option 2) Leave them as is, but with some basic cleaning (eliminating the few units that do cause issues).
As the data guy I'm leaning toward Option 1. None of these units are on a RAT or RAT Generator meaning you only see them with custom made RATs or adding manually. The do appear in MekHQ as refit options. Tons of these units aren't valid as they've been made with construction rules pre Tech Manual. Basically they would become an optional download for players.
In both cases these folders won't receive any official support from the devs.