I think it's an interesting idea and possibly useful for people who want to tweak their own Magitech to have a chance to test the new stuff out before they add it in, a kind of repository of new Tech units with a Trial mode added in!
The Walls BTW are probably just for GAE. Note this feature is/was experimental and it is currently implemented nowhere. I pretty much think they're not supposed to do anything though. The reason it needed extra coding was for the AI to know how to deal with it - it does not need to bring a whole long wall down, just break through it so the units can go past it. There were also plans to make it possible to make units walk on top of it (like its defenders).
There have been additions to Magic. One is the Evil Dragon that Titi added to his version of Magic (I don't remember where it comes from or who did it though).
I don't think you will find enough units to add to each of Megapack's factions though.
Overall, I think it's nice you did this, wyvern.